Pioneer RT-707 Capacitor Upgrade and Service
- Thread starter Trevor White
- Start date
Trevor White
Classic not Plastic
Unfortunately mate I found that with the 20 thou spacers in place the machine would not record, or playback, properly, and not just according to the instruments, but you could hear the drop outs as well!. The Right Channel was VERY uneven in it's performance, except on the thinnest tapes. At least with the 10 thou spacers the recording and playback performance of all the tapes, except SM911 was even, although as you say not perfect, according to the instruments, audibly they were very good. I'm not sure I could put up with it's poor right channel behavior to allow it to 'run in' with the 20 thou spacers in place.
Additionally, although I measured the front to back fall of the head base plate, I cannot say with any certainty that the heads themselves are mounted 'parallel' to the base plate. When I cleaned and inspected the heads very closely under strong magnification the trapezoid wear pattern is not that great.
I think I would rather use the machine in it's current state for a while, and perhaps consider going back to the 20 thou spacers in the future if it wears in using the 10 thou spacers. As it stands now the machines performance is excellent, although I still have to completely sort out the HF Bias, which thanks to Smurfer's post above, I am probably better armed to do.
Cheers.
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Trevor White
Classic not Plastic
Hello again Everyone,
So today I have been having another go at the BIAS adjustments. Thanks to Smurfer77 for providing the formula to calculate the difference in millivolts required to change by a set dB value.
As I suspected my attempts at doing the BIAS adjustments previously were compromised by my invalid calculations of the millivolt levels I was trying to adjust to. Previously when measuring the Peak level for the 1KHz recorded tone I was subtracting only 9mV. It turned out that I should have been using about 22mV. So I went back to basics today and re-performed the BIAS adjustment. My 'Peak' levels were very similar to the values I noted previously, but this time I was able to overbias (turn the VR's anti-clockwise) by the correct amount to achieve the specified -0.2dB overbias, which as I said was a drop in level on the meter of approximately 22mV.
Then I turned again to the BIAS levels for the -20dB tones. The 1KHz at -20dB showed levels of approx 42mV for the left channel and 36mV for the right channel.
The initial values for the 15KHz tone at -20dB were 42mV for the left channel and 38mV for the right channel. So nowhere near the -3dB the manual specifies!
I then used the formula to calculate that for a -3dB drop in level from 42mV and 36mV I would need to go down to 21mV and 18mV for the left and right channels respectively. Now I don't know just what is going on here, but by turning the VR's anti-clockwise I could not get anywhere near these levels. In fact the VR's ran out of adjustment before I could get to 21mV or 18mV for the left and right!
So it was back to the initial BIAS adjustment and resetting the VR's back to the -0.2dB overbias again. Once again the 1KHz at -20dB gave me 42mV and 36mV for the left and right respectively. I remember from reading Smurfer's attempt at this that he also settled for a level reduction of only -1dB, so I calculated that to achieve a similar result I would need to drop the 15KHz at -20dB levels down to 33-34mV and 28-29mV for left and right.
I had a go at that adjustment and was easily able to drop the levels down by approximately 1dB.
This might simply have to do! It means though that my primary BIAS level adjustment is now around -.9dB to -.8dB, not the -.2dB specified in the manual.
I'm just not clear on why the High Frequency BIAS adjustment is not behaving as I expected. I wonder if it is to do with the modern tapes we are using to perform these tests. I don't know just what the original Pioneer STD-502 tape actually was. Perhaps it's High Frequency behavior was different. I guess the objective here is to not over saturate the tape at these high frequencies, but on my machine I think this -1dB drop in level at 15KHz will just have to do.
Now I'm off to do the final step, Recording Level adjustment.
So today I have been having another go at the BIAS adjustments. Thanks to Smurfer77 for providing the formula to calculate the difference in millivolts required to change by a set dB value.
As I suspected my attempts at doing the BIAS adjustments previously were compromised by my invalid calculations of the millivolt levels I was trying to adjust to. Previously when measuring the Peak level for the 1KHz recorded tone I was subtracting only 9mV. It turned out that I should have been using about 22mV. So I went back to basics today and re-performed the BIAS adjustment. My 'Peak' levels were very similar to the values I noted previously, but this time I was able to overbias (turn the VR's anti-clockwise) by the correct amount to achieve the specified -0.2dB overbias, which as I said was a drop in level on the meter of approximately 22mV.
Then I turned again to the BIAS levels for the -20dB tones. The 1KHz at -20dB showed levels of approx 42mV for the left channel and 36mV for the right channel.
The initial values for the 15KHz tone at -20dB were 42mV for the left channel and 38mV for the right channel. So nowhere near the -3dB the manual specifies!
I then used the formula to calculate that for a -3dB drop in level from 42mV and 36mV I would need to go down to 21mV and 18mV for the left and right channels respectively. Now I don't know just what is going on here, but by turning the VR's anti-clockwise I could not get anywhere near these levels. In fact the VR's ran out of adjustment before I could get to 21mV or 18mV for the left and right!
So it was back to the initial BIAS adjustment and resetting the VR's back to the -0.2dB overbias again. Once again the 1KHz at -20dB gave me 42mV and 36mV for the left and right respectively. I remember from reading Smurfer's attempt at this that he also settled for a level reduction of only -1dB, so I calculated that to achieve a similar result I would need to drop the 15KHz at -20dB levels down to 33-34mV and 28-29mV for left and right.
I had a go at that adjustment and was easily able to drop the levels down by approximately 1dB.
This might simply have to do! It means though that my primary BIAS level adjustment is now around -.9dB to -.8dB, not the -.2dB specified in the manual.
I'm just not clear on why the High Frequency BIAS adjustment is not behaving as I expected. I wonder if it is to do with the modern tapes we are using to perform these tests. I don't know just what the original Pioneer STD-502 tape actually was. Perhaps it's High Frequency behavior was different. I guess the objective here is to not over saturate the tape at these high frequencies, but on my machine I think this -1dB drop in level at 15KHz will just have to do.
Now I'm off to do the final step, Recording Level adjustment.
Trevor White
Classic not Plastic
Yes, indeed. Both switches depressed, that is in LH mode. I imagine it would be easy to make that mistake!
Cheers.
Trevor White
Classic not Plastic
Hi everyone,
I have been busy over the last day and a bit, so here is the latest catch up
First was to finalise the electronic adjustments with the Recording Level setting. Once again you have to setup a 1KHz signal at -10db (316mV).
Then set the Line Input pots to give a level of -7dB (450mV) at output. And finally whilst recording and playing back the 1KHz tone setting the Recording Level VR's (VR301 and VR302) to also produce -7db (450mV) at output.
After making this adjustment I was pleased to see that the VU meters were nicely at Zero, just as we should expect.
So after completing all the adjustments I performed some actual recording tests using a variety of tapes. The results from the newer high grade tapes, Mulann LPR35 and Quantegy/Ampex 456 was nothing short of astonishing. For a machine of it's age, with head wear, it's ability to make recordings that are virtually indistinguishable from the original source is very, very impressive. It sounds fantastic. With older tapes like BASF LP35LH and Scotch 207, it's performance was still exceptional, although the output from those tapes is not as high, none the less very impressive sound, both at 7.5ips and even 3.75ips. In fact this machine can make recordings at 3.75ips that rival what my Sony can do at 7.5ips.
Then this morning I received a nice surprise at the local Post Office.
A nice second hand Extech 475040 Digital Force Gauge. I was lucky to find this unit, in its original case with all it's accessories in great condition. With a new set of batteries I tested it with some known calibration weights, and it was exactly correct.
I have been waiting for weeks to get hold of something like this as I have long suspected that part of my tape tracking problems may be related to poor back tension. So, now I was armed with something I could use to determine once and for all just what is going on.
Here is an image of the two main big resistors at their original settings.
Take note of the positions of the adjustable taps.
So here is the all important measurement, Forward Play - Back Tension.
As you can see the reading is 33 grams. The specs in the manual call for 70 to 80 grams. So there is a part of my problem with tapes tracking across the heads.
I proceeded to adjust the moveable tap until I got a reading between 70 and 80 grams. It took a few iterations to get this right. At all times being extremely careful with those old wire wound resistors.
Here is the end result. Much better!
I proceeded to then perform the other back tension tests. Below is a list of what I found for each, and what I was able to adjust to.
Forward Play - Back Tension
Original: 33 - 35
Adjusted: 75 - 80
Reverse Play - Back Tension
Original: 45 - 50
Adjusted: 75 - 80
Forward Play - Take Up Tension
Original: 130 - 135
Adjusted: No Change, within spec.
Reverse Play - Take Up Tension
Original: 155 - 160
Adjusted: No Change, within spec.
Rewind - Back Tension
Original: 10 - 15
Adjusted: 40 - 45
Fast Forward - Back Tension (This is controlled by the Rewind Back Tension resistor)
Original: 0 - 5
After adjusting Rewind: 15 - 20
I then moved on to checking the Pinch Roller pressure. This involves looping a piece of line around the Pinch Roller actuator and measuring the load required to stop the tape, ie: separate the Pinch Roller from the Capstan. The Extech 475040 has a nice feature that allows it to record a peak value and keep that displayed. That was perfect for performing this test.
Getting ready.
And after pulling on the meter to stop the Pinch Roller.
The manual says that a load of between 1.3kg and 1.6kg is required here. 1.375kg will do me nicely.
Finally, I checked the brakes.
Here I am checking the supply reel side.
Once again I have used the Peak Hold mode to measure the brake load. The manual says a load of 300 to 400 grams is required.
Supply Reel - Brake Tension
Original: 401
Adjusted: No Change
Take Up Reel - Brake Tension
Original: 285
Adjusted: 358
Adjusting the Take Up Reel brake actually involved taking it apart and cleaning the brake felt, then setting the load spring to a higher level.
Here is a final shot showing the two big resistors, after I made my back tension adjustments. I had to move those taps quite a bit. Although the reel motors seem AOK, so I don't know why the back tensions were so far out of whack.
After doing all of this I then checked how the tapes were running across the heads. Of particular interest was the troublesome Mulann SM911. To my great relief the SM911 now tracked across the heads evenly. No sign of buckling or lifting that I was seeing before. The acid test of course was to make a recording. The SM911 sounded fantastic, no sign of the dropouts that plagued it previously (with the tape lifting from the heads)
So I'm now left wondering if I should go back and re-verify my Azimuth and other adjustments, just to see if the additional back tension has changed the way the tape travels across the heads.
In any event, the Extech 475040 was worth it's weight in gold, and certainly worth the wait to get it all the way down here from the U.S.
Bye for Now
I have been busy over the last day and a bit, so here is the latest catch up
First was to finalise the electronic adjustments with the Recording Level setting. Once again you have to setup a 1KHz signal at -10db (316mV).
Then set the Line Input pots to give a level of -7dB (450mV) at output. And finally whilst recording and playing back the 1KHz tone setting the Recording Level VR's (VR301 and VR302) to also produce -7db (450mV) at output.
After making this adjustment I was pleased to see that the VU meters were nicely at Zero, just as we should expect.
So after completing all the adjustments I performed some actual recording tests using a variety of tapes. The results from the newer high grade tapes, Mulann LPR35 and Quantegy/Ampex 456 was nothing short of astonishing. For a machine of it's age, with head wear, it's ability to make recordings that are virtually indistinguishable from the original source is very, very impressive. It sounds fantastic. With older tapes like BASF LP35LH and Scotch 207, it's performance was still exceptional, although the output from those tapes is not as high, none the less very impressive sound, both at 7.5ips and even 3.75ips. In fact this machine can make recordings at 3.75ips that rival what my Sony can do at 7.5ips.
Then this morning I received a nice surprise at the local Post Office.
A nice second hand Extech 475040 Digital Force Gauge. I was lucky to find this unit, in its original case with all it's accessories in great condition. With a new set of batteries I tested it with some known calibration weights, and it was exactly correct.
I have been waiting for weeks to get hold of something like this as I have long suspected that part of my tape tracking problems may be related to poor back tension. So, now I was armed with something I could use to determine once and for all just what is going on.
Here is an image of the two main big resistors at their original settings.
Take note of the positions of the adjustable taps.
So here is the all important measurement, Forward Play - Back Tension.
As you can see the reading is 33 grams. The specs in the manual call for 70 to 80 grams. So there is a part of my problem with tapes tracking across the heads.
I proceeded to adjust the moveable tap until I got a reading between 70 and 80 grams. It took a few iterations to get this right. At all times being extremely careful with those old wire wound resistors.
Here is the end result. Much better!
I proceeded to then perform the other back tension tests. Below is a list of what I found for each, and what I was able to adjust to.
Forward Play - Back Tension
Original: 33 - 35
Adjusted: 75 - 80
Reverse Play - Back Tension
Original: 45 - 50
Adjusted: 75 - 80
Forward Play - Take Up Tension
Original: 130 - 135
Adjusted: No Change, within spec.
Reverse Play - Take Up Tension
Original: 155 - 160
Adjusted: No Change, within spec.
Rewind - Back Tension
Original: 10 - 15
Adjusted: 40 - 45
Fast Forward - Back Tension (This is controlled by the Rewind Back Tension resistor)
Original: 0 - 5
After adjusting Rewind: 15 - 20
I then moved on to checking the Pinch Roller pressure. This involves looping a piece of line around the Pinch Roller actuator and measuring the load required to stop the tape, ie: separate the Pinch Roller from the Capstan. The Extech 475040 has a nice feature that allows it to record a peak value and keep that displayed. That was perfect for performing this test.
Getting ready.
And after pulling on the meter to stop the Pinch Roller.
The manual says that a load of between 1.3kg and 1.6kg is required here. 1.375kg will do me nicely.
Finally, I checked the brakes.
Here I am checking the supply reel side.
Once again I have used the Peak Hold mode to measure the brake load. The manual says a load of 300 to 400 grams is required.
Supply Reel - Brake Tension
Original: 401
Adjusted: No Change
Take Up Reel - Brake Tension
Original: 285
Adjusted: 358
Adjusting the Take Up Reel brake actually involved taking it apart and cleaning the brake felt, then setting the load spring to a higher level.
Here is a final shot showing the two big resistors, after I made my back tension adjustments. I had to move those taps quite a bit. Although the reel motors seem AOK, so I don't know why the back tensions were so far out of whack.
After doing all of this I then checked how the tapes were running across the heads. Of particular interest was the troublesome Mulann SM911. To my great relief the SM911 now tracked across the heads evenly. No sign of buckling or lifting that I was seeing before. The acid test of course was to make a recording. The SM911 sounded fantastic, no sign of the dropouts that plagued it previously (with the tape lifting from the heads)
So I'm now left wondering if I should go back and re-verify my Azimuth and other adjustments, just to see if the additional back tension has changed the way the tape travels across the heads.
In any event, the Extech 475040 was worth it's weight in gold, and certainly worth the wait to get it all the way down here from the U.S.
Bye for Now
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smurfer77
Super Member
Trev, The Extech gives your a bit of a shock when you first see the sticker price, but as you probably found out they can be had from time to time as deeply discounted rates.
Great news that the tension sorted out your tracking and great detail in the last post is really useful because those particular adjustments are ones that I glossed over or barely mentioned in my thread. Good work.
Great news that the tension sorted out your tracking and great detail in the last post is really useful because those particular adjustments are ones that I glossed over or barely mentioned in my thread. Good work.
nh36000
Too many notes!!!
Gents;
I've been reading this thread all along and every week or so. Looking at post #140, I wonder if you are making a mistake.
'Over Bias' is turning the pots clockwise past peak. 'Over' biasing also drops high frequency, as well as 'under' biasing, using high Bias tape. I don't have a 707 here to know, and maybe they are different than a TEAC.
I bring this up as, in a conversation with another person, I wrote that the highs were scratchy and distorted sounding. The reply was, 'not enough bias'. And bumping up the bias cleaned up the highs nicely.
Like smurfer has said, you need to adjust bias to get record EQ in range. To adjust bias for the sake of high frequencies isn't exactly the right thing to do. And I know, the less than pro decks like the TEAC 3300s I have, that is just what the SMs tell you to do. Set record bias and EQ at 3 3/4 ips, then record at 7 1/2 ips, and adjust frequency response with the bias adjustments.
Maybe a 707 does handle all that, differently.
All for now. One very interesting thread, though. I'll keep reading.
Lu.
I've been reading this thread all along and every week or so. Looking at post #140, I wonder if you are making a mistake.
'Over Bias' is turning the pots clockwise past peak. 'Over' biasing also drops high frequency, as well as 'under' biasing, using high Bias tape. I don't have a 707 here to know, and maybe they are different than a TEAC.
I bring this up as, in a conversation with another person, I wrote that the highs were scratchy and distorted sounding. The reply was, 'not enough bias'. And bumping up the bias cleaned up the highs nicely.
Like smurfer has said, you need to adjust bias to get record EQ in range. To adjust bias for the sake of high frequencies isn't exactly the right thing to do. And I know, the less than pro decks like the TEAC 3300s I have, that is just what the SMs tell you to do. Set record bias and EQ at 3 3/4 ips, then record at 7 1/2 ips, and adjust frequency response with the bias adjustments.
Maybe a 707 does handle all that, differently.
All for now. One very interesting thread, though. I'll keep reading.
Lu.
Trevor White
Classic not Plastic
Hi there nh3600.
The issue we found with the 707 was that turning the Bias VR's clockwise DID NOT increase bias. It was the opposite and actually decreased it. All that Smurfer and I have done is to reverse the Pioneer instructions so that turning anti-clockwise is increasing the bias. Then turning a little beyond the peak, anti-clockwise, takes you into over-bias.
Anyway, the machine sounds great, so something must be right.
Cheers.
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Trevor White
Classic not Plastic
Hi there mate,
Yes I was lucky to find the Extech and was able to pick it up for $150 USD. I have seen them for a LOT more that that! It was certainly worth the effort in getting one that's for sure.
I was surprised to find the back tensions as low as they were. Did you do this adjustment of your 707? Can you recall what your back tension on Forward/Reverse Play were?
Cheers.
smurfer77
Super Member
Trevor,
My Exctech force gauge is a new addition to my toolbox. When I did the 707 originally I was using spring gauges, which in principle can be fine, but mine were awful kitchen grade stuff
. So that is why I didn't report my findings, since I had little faith in them. My 707 is due first it's first annual service so I will report in the thread when I do it. Will also be interested to see if the electrical calibration has drifted (or my heads have worn down much!).
smurfer77
Super Member
For sure, over and underbias drop the high frequency on either side of the peak. What might not have been clear here is that the clockwise/anticlockwise clarification is that the conclusion I made was not from audio signal output, but I actually monitored the bias signal itself to be sure - discussed here.
Trevor White
Classic not Plastic
Hi All,
So I did in fact go back and re-check my Azimuth and then went through the whole calibration procedure all over again. This time (after changing the back tensions) I found that the Left and Right channel performances were much more even, and closer together, that is, not as large a difference in levels between Left and Right in many of the tests. I also found that the output level of the Forward Playback head was a lot better and now matched almost exactly the output levels of the Reverse Playback head.
After doing all the adjustments again I then spent quite some time performing some recording tests, trying out various different types of tape and making notes on how they performed in regard to the setting of the Bias and EQ switches. In the RT-707 manual there is a little table offering suggestions for the Bias and EQ settings for a variety of tapes. Having now Biased the machine for LPR35, I found that the settings for older tapes like the Scotch 207 and BASF LP35/LH no longer applied. Originally these tapes were treated as 'LH' but I find that now I need to set the Bias switch to Standard to get some decent top end out of them. Not that it really matters, most of my tapes that I use now are Quantegy 456 and Mulann LPR35.
Now, this brings me to a question for those of you with 707's (Smurfer). After having the machine in use for quite some time this afternoon I noticed that the Supply Reel Motor was quite warm, almost hot in fact. I had been recording/playing and also some Fast Forward and Rewind of whole 1800' tapes. Have any of you ever checked or noticed what sort of temperatures the Supply Reel and Take Up Reel motors run at in your machines? I know Smurfer took some FLIR pictures of his machine but I don't think the motors were included.
Thanks.
EDIT: I should perhaps mention that the ambient temperature in the room was about 26 degrees C. I've also just started a test (with the motors cold) where I will play an 1800' tape through to the end. No FF or RW. Just to see if it is playback that is causing the motor temp.
EDIT2: I have just played an 1800' tape all the way through one side. So what's that? 45 minutes? Anyway, I have a thermocouple that I can connect to my DMM and that reports that both of the Reel Motors are 42 degrees C. That's pretty warm, but you can easily touch the motor casings without leaving skin behind
EDIT3: OK I have just performed a Rewind / Fast Forward / Rewind of the 1800' tape. The Supply Reel motor got up to about 52 degrees C, whilst the Take Up Reel motor got up to 47 degrees.
Do you all think that is too warm? Smurfer, do you have any FLIR images of your machine whilst it was open that show the Reel Motors?
So I did in fact go back and re-check my Azimuth and then went through the whole calibration procedure all over again. This time (after changing the back tensions) I found that the Left and Right channel performances were much more even, and closer together, that is, not as large a difference in levels between Left and Right in many of the tests. I also found that the output level of the Forward Playback head was a lot better and now matched almost exactly the output levels of the Reverse Playback head.
After doing all the adjustments again I then spent quite some time performing some recording tests, trying out various different types of tape and making notes on how they performed in regard to the setting of the Bias and EQ switches. In the RT-707 manual there is a little table offering suggestions for the Bias and EQ settings for a variety of tapes. Having now Biased the machine for LPR35, I found that the settings for older tapes like the Scotch 207 and BASF LP35/LH no longer applied. Originally these tapes were treated as 'LH' but I find that now I need to set the Bias switch to Standard to get some decent top end out of them. Not that it really matters, most of my tapes that I use now are Quantegy 456 and Mulann LPR35.
Now, this brings me to a question for those of you with 707's (Smurfer). After having the machine in use for quite some time this afternoon I noticed that the Supply Reel Motor was quite warm, almost hot in fact. I had been recording/playing and also some Fast Forward and Rewind of whole 1800' tapes. Have any of you ever checked or noticed what sort of temperatures the Supply Reel and Take Up Reel motors run at in your machines? I know Smurfer took some FLIR pictures of his machine but I don't think the motors were included.
Thanks.
EDIT: I should perhaps mention that the ambient temperature in the room was about 26 degrees C. I've also just started a test (with the motors cold) where I will play an 1800' tape through to the end. No FF or RW. Just to see if it is playback that is causing the motor temp.
EDIT2: I have just played an 1800' tape all the way through one side. So what's that? 45 minutes? Anyway, I have a thermocouple that I can connect to my DMM and that reports that both of the Reel Motors are 42 degrees C. That's pretty warm, but you can easily touch the motor casings without leaving skin behind
EDIT3: OK I have just performed a Rewind / Fast Forward / Rewind of the 1800' tape. The Supply Reel motor got up to about 52 degrees C, whilst the Take Up Reel motor got up to 47 degrees.
Do you all think that is too warm? Smurfer, do you have any FLIR images of your machine whilst it was open that show the Reel Motors?
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smurfer77
Super Member
I think your reel motors are fine. They will get a bit warm with use. On some other models it is a bigger problem form what I recall.
I am at the tail end of making a 1800' mix 7.5IPS mix tape right now. I didn't pull out the FLIR but I grabbed the IR thermometer and I measure supply reel at just under 40 C and the take-up reel just over over C. This feel about right according to my finger test. If I probe inside the gaps I can detect even higher temperatures. Yes, I would expect them to get even hotter after a RWD/FWD of a tape. I think you are fine. However, I must admit have always cringed a bit when I see these in racks, or not in a rack but with something on top limiting airflow; I had long ago decided to never rack my 707 no matter how cool it might look.
I am at the tail end of making a 1800' mix 7.5IPS mix tape right now. I didn't pull out the FLIR but I grabbed the IR thermometer and I measure supply reel at just under 40 C and the take-up reel just over over C. This feel about right according to my finger test. If I probe inside the gaps I can detect even higher temperatures. Yes, I would expect them to get even hotter after a RWD/FWD of a tape. I think you are fine. However, I must admit have always cringed a bit when I see these in racks, or not in a rack but with something on top limiting airflow; I had long ago decided to never rack my 707 no matter how cool it might look.
Trevor White
Classic not Plastic
That's great mate, thanks for checking that. It is good to have confirmation that my motors are behaving in much the same way as yours. I was initially concerned that my increase in the back tension settings may have caused some significant extra loading. What is the ambient temperature there for you?
I absolutely agree with your point about not racking these machines. As soon as I got this one of mine I quickly realised that I would need to locate it in my cabinets with plenty of air space above the machine. Like you though, I have seen pictures of these with books and all kinds of stuff stacked on top!
I have just about reached the point of reassembling the machine! I really appreciate the help both you and GPS16 have provided during this journey. It has been great fun and very rewarding.
Cheers.
smurfer77
Super Member
Trev, sorry I should have mentioned, my ambient temperature is about 15 C today, so I was not surprised my reel motors are running a little cooler than yours
. I will update on any changes to tension/temperature in my thread, after I recalibrate my 707 during upcoming servicing.
Trevor White
Classic not Plastic
Trev, sorry I should have mentioned, my ambient temperature is about 15 C today, so I was not surprised my reel motors are running a little cooler than yours
Ah, that helps. My ambient at the moment is about 26 - 27 degrees C. Going to be 35 outside today, phew!
Right now I am just conducting an experiment where I am performing the Bias/Response adjustment using some old world tape. A brand new roll of Scotch 207, just to see if the variations in bias specs we have seen may have anything to do with the tape stock itself. So far, quite interesting results. The bias levels on the Scotch 207 are much lower than on the Mulann LPR35. I will report with more details later.
Cheers.
Trevor White
Classic not Plastic
OK, so just as an exercise I had a go at setting the Bias adjustments for a new/old stock reel of Scotch 207. The output levels from the 207 were way lower than from the newer stock tapes. I was able to get the bias setup OK, but once again found that there was no way to get the 15KHz -20dB signal recorded at -3dB from the 1KHz -20dB signal. I again set it for approx -1dB.
I then performed a recording test on both the 207 and on some LPR35. The results were less than impressive. The 207 sounded dull and lacked high end, even with the BIAS and EQ switches in the STD position. In the LH position, where they were biased, the 207 sounded very ordinary.
So I deemed that experiment a failure and have now performed the Bias adjustments yet again using the Mulann LPR35, with which the machine works and sounds fantastic. In fact with the Bias set for the LPR35 the old Scotch 207 then sounds good with the BIAS and EQ switches in the STD position. It's all very confusing
Cheers.
I then performed a recording test on both the 207 and on some LPR35. The results were less than impressive. The 207 sounded dull and lacked high end, even with the BIAS and EQ switches in the STD position. In the LH position, where they were biased, the 207 sounded very ordinary.
So I deemed that experiment a failure and have now performed the Bias adjustments yet again using the Mulann LPR35, with which the machine works and sounds fantastic. In fact with the Bias set for the LPR35 the old Scotch 207 then sounds good with the BIAS and EQ switches in the STD position. It's all very confusing
Cheers.
Trevor White
Classic not Plastic
Hello everyone.
So, I think my project on the RT-707 has come to a successful conclusion. Definitely a case of 'with a little help from my friends'. Thank you to all who contributed to this thread. I hope the information and data provided may help others of you considering rebuilding an RT-707.
The first job though was to put the machine back together!
Here the base plate is being refitted.
And the rear back plate.
I have refitted the plastic shroud for the RCA inputs etc.
But this was more difficult than I expected.
If you look at the top left of this picture, the Grey, Yellow and White wire bundles needed to be carefully moved out of the way as they obstructed the plastic shroud from fitting easily.
Final view inside the machine with many of it's new components visible.
Finally the face plate has been refitted.
When doing this be sure that the VU meters locate properly. I have actually seen 707's being sold as 'refurbished' but with the VU meters clearly out of square, which must mean that they get crushed by the facia when it is screwed down
Finally with the outer casing refitted.
And here it is, located in it's new home and working well.
Alongside of my other stereo gear. I don't have a lot, but the Sony was purchased in 1974, and the Luxman Amp in 1984. Both still work perfectly.
I hope you have all enjoyed this journey as much as I have. It's been great fun, and very educational. Where I live getting quality technicians to work on vintage gear like this is all but impossible. It has been a very expensive exercise, as I did not have any of the special instruments required, but has been well worth the effort to do it myself. And those instruments will come in useful for lots of other projects I'm sure.
I shall update this thread as time goes by with any future work or repairs.
Bye for Now,
Trevor
So, I think my project on the RT-707 has come to a successful conclusion. Definitely a case of 'with a little help from my friends'. Thank you to all who contributed to this thread. I hope the information and data provided may help others of you considering rebuilding an RT-707.
The first job though was to put the machine back together!
Here the base plate is being refitted.
And the rear back plate.
I have refitted the plastic shroud for the RCA inputs etc.
But this was more difficult than I expected.
If you look at the top left of this picture, the Grey, Yellow and White wire bundles needed to be carefully moved out of the way as they obstructed the plastic shroud from fitting easily.
Final view inside the machine with many of it's new components visible.
Finally the face plate has been refitted.
When doing this be sure that the VU meters locate properly. I have actually seen 707's being sold as 'refurbished' but with the VU meters clearly out of square, which must mean that they get crushed by the facia when it is screwed down
Finally with the outer casing refitted.
And here it is, located in it's new home and working well.
Alongside of my other stereo gear. I don't have a lot, but the Sony was purchased in 1974, and the Luxman Amp in 1984. Both still work perfectly.
I hope you have all enjoyed this journey as much as I have. It's been great fun, and very educational. Where I live getting quality technicians to work on vintage gear like this is all but impossible. It has been a very expensive exercise, as I did not have any of the special instruments required, but has been well worth the effort to do it myself. And those instruments will come in useful for lots of other projects I'm sure.
I shall update this thread as time goes by with any future work or repairs.
Bye for Now,
Trevor
