Pioneer RT-707 Capacitor Upgrade and Service

Hi Trevor,

noticed in one of your photos, you have the machine running. The supply reel is plastic and the take up is metal. Do NOT do this. I have stated this elsewhere on the forum and things were beginning to get heated so I shut up!!!. Suffice it to say....... Read the first paragraph on page 7 of the USER manual headed Threading The Tape.

There will be no problem during play. It is the stopping from full speed during a wind when it will rear it's ugly head and believe me, it will be catastrophic. The tape in question will be ruined.

For that particular paragraph I agree ENTIRELY!!!

Cheers.

GPS16
 
Thanks mate. I have in fact noted that statement in the manual, but always wondered why? Is it anything to do with static discharge, or perhaps inertial mass difference?

I will take note of this. I have some empty plastic reels I can use.

EDIT: I just weighed a couple of empty reels. An empty Scotch plastic reel was 100 grams, my empty Sony plastic reel was also 100 grams, whilst my empty PR85 Pioneer Metal Reel was 130 grams, give or take a gram for each of them. (These were all 7" reels)
 
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Hi Trevor,

it is to do with Rotational Inertia. The reels act as flywheels. The size and material need to matched so that the only difference is the wrap size of the tape. This is taken into account easily by the differential brakes. What ever the direction, the reel which is feeding the tape is always more heavily braked than the reel receiving the tape. This is done by design to stop spillage. The reel tables are on the end of motors!!! None of your single motor belt driven "I can rewind it quicker with my finger" here.

The overall weight of the reel is not necessarily the point. It is the distribution and the distance from the centre which makes the difference. If the extra 30 grams is concentrated at the outside edge then bingo!!!

The rotational inertia is proportional to the square of the rotational speed so twice the speed gives 4 times the rotational energy. This could easily be outside of the scope of the differential brakes. A fast moving loop of tape is what results and it goes anywhere it pleases. Furthermore, there is NOTHING you can do about it and any intervention by you will make matters worse. Sod's Law will then dictate that the tape in question is the one in your collection that you treasure, that is why it was on the machine in the first place!!!

If you have a Metal Reel with tape on it which is full and you mount it with a Plastic take up reel. You then want to listen to the second track in not the first so you FF the tape to the relevant counter position. This will still leave a large wrap on the metal reel and not a lot on the plastic. The problem therefore manifests. The heavy braking on the reel supplying the tape is a full one and a metal reel with pretty much the MOST rotational Inertia you can get. The take up reel is plastic with hardly any tape which is the LEAST rotational inertia. If the lower braking on the take up reel can stop the virtually empty plastic reel quicker than the more heavily braked metal reel which is virtually full. Where does the tape from the still spinning supply reel go when there is no spinning take up reel to receive it? You will do this ONCE!!!!!!

As the paragraph states. Size for Size AND Material for Material. The differential brakes then only need to deal with the difference in size of tape wrap. The other variables are in balance and cancel out.

I deal with Turbo Vacuum Pumps at work. These can be spinning at 48,000 RPM. The health and safety bulletins fill a folder. As one type of pump can only be fixed by a clamp (6 actually) which sits in a groove to mount the pump to the Vacuum System, if there is a catastrophic rotor crash the inertia of the spinning rotor tries to rip the pump off the machine and throw it against the wall. One safety bulletin advised that all quick release aluminium clamps had to be replaced with stainless steel ones. The aluminium ones could be destroyed and act like a grenade. While this example is a bit "Extreme!!!" I felt I had to do a bit of research into the maths involved to "cover my backside" as it were for negligence.

There are photos on this forum with plastic 7" supply reels and a 10.5" Metal take up reel. They made me wince!!!!

Cheers.

GPS16
 
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GPS16 wrote: "There are photos on this forum with plastic 7" supply reels and a 10.5" Metal take up reel."
On a RT-707? Link, please...

Chip
 
Hi Chip,

try the "What are you listening to right now" threads!!

I've seen them but can't remember where!!!

GPS16
 
Very good music and SQ also.

3c8e13205f97a51b42aeabaa66fedee4.jpg


b64a2a7e7e49995c8adf79e2f11974bf.jpg


And explanation for the 1960's audiophile!!

0c7293f63130f689956f926d908dbc52.jpg


There are also others!!!

The comment about the 10.5" reels was just that, a comment!!! The fact that it did not apply to a 707 had occurred!!!

The underlying advice still stands. Same Size/Same Material. In the RT707 case you still have the choice of 7", 5" and 3" (4" as well but you might need to search for them).

GPS16
 
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Hi All, here we go with the next stage.

This time I begin working on the final section of the machine, The Playback Amplifier board (RWF-069) and it's two daughter boards the Head Amplifiers (RWF-070).

First step was to inspect the Playback Amp and then remove the two RWF-070 boards.

Here is the RWF-069 board in situ with all the original components.
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Here are the two RWF-070 Head Amplifiers.
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And finally after careful de-soldering here they are out of the machine with their original components. Take note of the two Orange caps on each board which are once again those 'Low Leakage' caps.
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Here is the back of the RWF-069 board after removing the RWF-070 boards. These boards are coated in some clear sticky goo that makes the devil's own mess when heated with a soldering iron. This picture is after cleaning up the area around the foil pads.
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This is the first of the RWF-070 boards I tackled. Fiddly but straightforward removal of the capacitors. I am changing only the Electrolytics and Ceramics. Here all the offenders have been removed.
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And now the rear of RWF-070. Once again a major cleanup required.
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Here is the finished RWF-070 with the removed components above.
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The finished article. You can see here that I have used WIMA film caps for the small value electrolytics, except for the very small (15pF) MURATA ceramics, the little blue drops. There are two Nichicon KL Low Leakage series in place of the original two Orange caps, and the remainder are Nichicon UFG's. The two FET transistors I left alone.
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Now both of the RWF-070's completed.
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The caps used on the Head Amplifier boards were:
4 x Nichicon FG 47uF 50V: http://www.mouser.com/ProductDetail/Nichicon/UFG1H470MPM
4 x Nichicon FG 100uF 16V: http://www.mouser.com/ProductDetail/Nichicon/UFG1C101MPM
4 x Nichicon FG 4.7uF 50V: http://mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
4 x Nichicon KL 10uF 25V: http://www.mouser.com/ProductDetail/Nichicon/UKL1E100KDDANA
4 x WIMA .047uf 100V: http://mouser.com/ProductDetail/WIMA/MKP2D024701C00JA00
4 x WIMA 100pF 100V: http://mouser.com/ProductDetail/WIMA/FKP2D001001D00JSSD
4 x MURATA 15pF 100V: http://www.mouser.com/ProductDetail/Murata-Electronics/RDE5C2A150J0P1H03B

The measured values of the old caps were:
Board 1
47uF 35V - 57 & 55
100uF 10V - 122 & 127
4.7uF 35V - 5.83 & 5.20
10uF 16V LL - 11.45 & 11.66
.047uF Ceramic - .037 & .043
100pF Ceramic - 97 & 98
15pF Ceramic - 15 & 16

Board 2
47uF 35V - 55 & 56
100uF 10V - 123 & 126
4.7uF 35V - 5.80 & 5.83
10uF 16V LL - 11.52 & 11.45
.047uF Ceramic - .045 & .047
100pF Ceramic - 93 & 97
15pF Ceramic - 17 & 15

That's it for this installment. Next is the main RWF-069, Playback Amplifier board. But first I need to get some Bourns multiturn trimmers etc.

Cheers for now.
 
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Hi phantomrebel,

This is a great, informative restoration thread (the best I've seen) and would hate to see it derailed.

credit where it is due. The similar restoration by Smurfer77 was also a cracking thread. Between Trevor and Smurfer any RT707 owner with Soldering skills can have a go!!! As long as they have the instrumentation to hand and is prepared to go to the expense of an alignment tape.

A smashing project for the Winter Months!!!!

GPS16
 
Trevor, I've been away for a few days and I come back and you have made tremendous progress! Thank you for posting parts details, which I may have missed in a few places (partly because I think it's good for folk to figure out how to make good decisions by themselves; it's part of the fun) - it will be useful for many. Regarding the UKL, I approve. The audio caps are not needed in many positions I used them in and in some places UKL or FC would have been better (but I had a lot of FG on hand). With the ceramics I encourage folks to make sure they use C0G type. About the carbon resistors I agree with GPS that this is a small thing in this case even though in principle there is more noise from carbon comp. Start working on tube amps (as GPS mentioned) and we can talk more about resistors. I am a fan of metal-film when I do replace though (they do not sound 'metallic' to me, and I see no reason why they should).

Again, outstanding work on both the rebuild and the thread. Just be careful, once I did the RT-707 just over a year ago, I'm now 5 r2r decks deep in my collection!

PS. I'm glad you got the calibration tapes. It's a big expense compared to the machine, but believe me, once you have it setup, you will be happy with the confidence that things are 100% as they should be. And who knows, you may use the tapes for other r2r decks in the future! I'm used mine on my Revox PR99 and now am about to use it again for the RT707 annual service
 
Trevor, I've been away for a few days and I come back and you have made tremendous progress! Thank you for posting parts details, which I may have missed in a few places (partly because I think it's good for folk to figure out how to make good decisions by themselves; it's part of the fun) - it will be useful for many. Regarding the UKL, I approve. The audio caps are not needed in many positions I used them in and in some places UKL or FC would have been better (but I had a lot of FG on hand). With the ceramics I encourage folks to make sure they use C0G type. About the carbon resistors I agree with GPS that this is a small thing in this case even though in principle there is more noise from carbon comp. Start working on tube amps (as GPS mentioned) and we can talk more about resistors. I am a fan of metal-film when I do replace though (they do not sound 'metallic' to me, and I see no reason why they should).

Again, outstanding work on both the rebuild and the thread. Just be careful, once I did the RT-707 just over a year ago, I'm now 5 r2r decks deep in my collection!

PS. I'm glad you got the calibration tapes. It's a big expense compared to the machine, but believe me, once you have it setup, you will be happy with the confidence that things are 100% as they should be. And who knows, you may use the tapes for other r2r decks in the future! I'm used mine on my Revox PR99 and now am about to use it again for the RT707 annual service

Cheers mate. I greatly appreciate your input.

It was your original thread on the RT-707 that gave me the confidence to have a go at this.

Trevor
 
Hi phantomrebel,

credit where it is due. The similar restoration by Smurfer77 was also a cracking thread.

A smashing project for the Winter Months!!!!

GPS16

Indeed, I have made reference to Smurfer's original thread in a number of places. But just in case others have not seen it, here is the link:
http://audiokarma.org/forums/index.php?threads/pioneer-rt-707-service-rebuild.702717/

It was this thread that gave me the information and confidence to have a go at this myself.
So a BIG thanks to Smurfer77 as well.
 
Hi All,

Well, I have been beavering away on my Playback Amp board, the RWF-069, which in my machine is actually an RWF-078. I expected that there would be differences between this board and the diagrams for the RWF-069 included in the manual. There were indeed a number of differences. In one case a capacitor shown on the diagram did not exist on the board, and three other capacitors were found on the board but not on the diagram! Also one cap on the diagram was shown as a .01uF Ceramic, but was in fact a .047uF Ceramic. So keeping a close watch on what is actually physically removed is always a wise idea.

Anyway I got to the end of replacing all the caps (pictures etc to follow soon) and I decided to also replace the pair of 2SC1344 and 2SA672 transistors. These are the same combinations as found on the MIC Amplifier board. I carefully removed the 2SC1344's and they were what they were supposed to be. BUT, when I removed the two 2SA672's they were actually something else.

The diagram showed a pair of 2SA672's, but in fact these were a pair of 2SA721. That came as a complete surprise. I tried to look up details for the 2SA721 and it had slightly lower current and voltage specs, compared to the 2SA672. The big difference was in the Transition Frequency (ft) and the Forward Current Transfer Ratio (hFE) figures. See below:

Type Designator: 2SA672
Material of Transistor: Si
Polarity: PNP
Maximum Collector Power Dissipation (Pc): 0.2 W
Maximum Collector-Base Voltage |Vcb|: 50 V
Maximum Collector-Emitter Voltage |Vce|: 50 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 0.2 A
Max. Operating Junction Temperature (Tj): 125 °C
Transition Frequency (ft): 40 MHz
Forward Current Transfer Ratio (hFE), MIN: 60
Noise Figure, dB: -
Package: SOT33

Type Designator: 2SA721
Material of Transistor: Si
Polarity: PNP
Maximum Collector Power Dissipation (Pc): 0.15 W
Maximum Collector-Base Voltage |Vcb|: 35 V
Maximum Collector-Emitter Voltage |Vce|: 35 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 0.1 A
Max. Operating Junction Temperature (Tj): 175 °C
Transition Frequency (ft): 250 MHz
Forward Current Transfer Ratio (hFE), MIN: 800
Noise Figure, dB: -
Package: TO92

The item that really stands out here is the hFE value, which is a minimum of 800 on the 2SA721.

I was a bit blind sided by this, and all the 'equivalence' lookups that I did, the KSC992F (used as a replacement for the 2SA672) was never listed as a possible replacement for the 2SA721. So instead I carefully remounted the 2SA721's and also put back the 2SC1344's.

Luckily when I tested the unit everything was fine, but I wonder just what role the 2SC1344 and the 2SA721's have in the Playback Amp.

Cheers, pictures and details on the RWF-078 (RWF-069) upgrade to follow.
 
Hi Trevor,

the transistors are the amplification just before the Line Output Sockets. The main Pre Amplification for the Heads is done on the small daughter PCB with the chips. The small PCB is also where the Playback equalisation is done with the FET.

In this case it is probably a good idea to stick with the originals. If the transistors are way different from the older circuit then there will probably be resistor changes associated with them. You will need the circuit for the new type PCB for this (obviously). The audio level at that point should comparatively high so noise should not really be an issue as the overall gains will not be too great. As with Op Amps, the overall gain is given by the resistors and transistors in combination. The high gain of the transistor you mentioned could be well throttled down.

Congratulations on getting a youngster for a machine!!!

Cheers.

GPS16
 
Hi Trevor,

the transistors are the amplification just before the Line Output Sockets. The main Pre Amplification for the Heads is done on the small daughter PCB with the chips. The small PCB is also where the Playback equalisation is done with the FET.

In this case it is probably a good idea to stick with the originals. If the transistors are way different from the older circuit then there will probably be resistor changes associated with them. You will need the circuit for the new type PCB for this (obviously). The audio level at that point should comparatively high so noise should not really be an issue as the overall gains will not be too great. As with Op Amps, the overall gain is given by the resistors and transistors in combination. The high gain of the transistor you mentioned could be well throttled down.

Congratulations on getting a youngster for a machine!!!

Cheers.

GPS16

Thanks mate. Yeah, as soon as I saw that the actual transistors used differed from the detail on the diagrams I immediately abandoned any plans to refresh those parts. Fortunately my removal and subsequent refitting of them has not seemed to do them any harm. (thank goodness)

Cheers,
Trevor
 
Hi everyone,

Here we go starting the final physical phase of the overhaul. This time I am re-capping the Playback Amplifier board. The two Head Amplifiers were done in the previous installment. Now to do the main Playback board itself.

The circuit diagrams in the Service Manual describe the Playback Amp as RWF-069, whilst in my machine this is actually an RWF-078. Some differences to be found no doubt. One that is immediately obvious is that the original RWF-069 supported a third daughter board, the RWX-155. This was the driver board for the VU meters, but this has now been incorporated into the main Playback Amp itself.

Due to these differences it is very important to proceed with this re-cap carefully. I basically did it one capacitor at a time so that I could verify the actual part against the Foil Side diagram from the manual. In doing this I found that the physical board held 4 more capacitors than indicated by the diagrams, 1 capacitor on the diagram did not exist on the board, and 1 capacitor had a different value than was indicated on the diagram.

So, without further ado, lets get on with it.

First I found it helpful to stand the machine on one end, with the Playback Amp at the top. I then dismounted the Control Assembly and it's alloy heat sink, moving them carefully out of they way. This gave a lot more clearance to the Playback Amp.

Here you can see the Control Assembly moved out of the way and loosely held by a cable tie.
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Here is the Foil side of the Playback Amp. Complete with plenty of that goo that these boards seem to be sealed with.
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And of course the component side, with the Head Amps still removed but all the capacitors replaced.
(This was supposed to be a shot with the original components still in place o_O)
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This board does have a pair of 2SC1344 transistors, and according to the diagrams, a pair of 2SA672 transistors. I had intended
to replace these as a matter of course, but discovered that the 2SA672 were actually 2SA721's. Based on this I re-installed the
2SC1344's and the 2SA721's and left well enough alone. (Thanks to GPS16 for help with this)
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After working through all of the capacitors, one at a time, I remounted the RWF-070 daughter boards. Here is the Foil side with them soldered back in.
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And of course the component side with everything replaced. If you look carefully you will see that I have used WIMA film caps
for the smaller value ceramics and there are also two Murata C0G ceramics as well (the little blue drops). All in all this was a
slightly fiddly process as some of the components, caps and transistors are quite closely packed. I did make a few mistakes
unsoldering component legs that should not have been :( But in the end it all came together nicely.
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The left overs. (Although my notes on the top of the diagram say 3 extra caps, there were actually 4. You can see 3 of them,
1 x 22uF 35V (originally 10V) and 2 x 22uF 50V (originally 35V), on the far left of the diagram where I have noted their
approximate locations. Also, one ceramic was noted on the diagram as a .01uF but was in fact a .047uF)
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The acid test. It still works! Sounds great too!
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Next step will be to replace the very finicky VR's for Bourns multi-turn units. That should make re-calibrating the machine a LOT easier.

For now though, here are the parts used on the Playback Amp:
1 x Nichicon FG 220uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H221MHM
5 x Nichicon FG 22uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H220MEM
4 x Nichicon FG 10uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H100MDM
2 x Nichicon FG 2.2uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H2R2MDM
13 x Nichicon FG 4.7uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H4R7MDM
1 x Nichicon FG 1uF 50V: https://www.mouser.com/ProductDetail/Nichicon/UFG1H010MDM
3 x WIMA .047uF 100V: http://mouser.com/ProductDetail/WIMA/MKP2D024701C00JA00
2 x Murata 22pF 100V: https://www.mouser.com/ProductDetail/Murata/RDE5C2A220J0P1H03B

And here are the measured values of the old electrolytics etc:
220uF 35V -- 252
22uF 35V -- 29, 27, 29
22uF 10V -- 29, 30
10uF 16V -- 14
10uF 35V -- 13, 15, 14
4.7uF 35V -- 5.99, 5.87, 5.85, 5.77, 6.05, 5.89, 5.78, 5.68, 5.26, 5.87, 5.73, 5.82, 5.78
2.2uF 50V -- 2.82, 2.72
1uF 50V -- 1.60, 1.45
.047uF Ceramic -- .040, .045, .052
22pF Ceramic -- 22, 23

That's it for this installment :)
 
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The next step in overhauling the Playback Amp is to replace the very tricky Variable Resistors used for the Playback EQ and Balance, and also for the VU meter levels.

First I would like to offer my gratitude to Smurfer77 whose advice and previous experience with the RT-707 has been invaluable to me, particularly with this step.

Anyway, first step was to order some of the fabulous little Bourns multi-turn VR's. The original parts called for 22K ohm, 33K ohm and 10K ohm VR's. In replacing them with the Bourns devices I chose 25K, 50K and 10K versions.

Here are the 25K and 50K Bourns VR's
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The first thing I did was make a diagram of my own showing how the original VR's were actually connected. I did this by studying the actual foil side of the board and tracing just what the 3 pins of each VR were actually connected to. I then made measurements of the resistances for all of the VR's whilst they were in circuit. I then carefully unsoldered each of them, measuring again their resistance values.

Here is my mud map, complete with the old VR's.
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For the Balance VR's, VR105 - VR108, in order to estimate the value to use in pre-setting the new VR's I calculated the % ratio of the old VR setting to its overall resistance. I then applied that percentage to the overall resistance on the Bourns VR and dialled up the adjuster to give that value. This will at least be close to the original calibration setting on these VR's.

As for the EQ VR's, VR101 - VR104, they are wired up somewhat differently. In each case the Wiper pin of the VR is also connected to one end of the VR. In this case it is the resistance value of the Wiper to the other pin that is of consequnce and I set the new VR's to match that original value.

Here is my final version of the diagram complete with my calculations.
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In any event the values dialed in at this point can only be approximations. Replacing these trimmers will require a full calibration using a reference calibration tape once everything is complete. For now though they get things fairly close.

And here we are with the VR101 - VR104 and VR105 - VR108 trimmers replaced.
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They are neat little things, and their 25 turn adjusters will make the calibration exercise much easier.
(If you look carefully you will see that the VR's for the VU meters have not yet been changed)
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Finally, testing the machine. To my considerable surprise it sounded fantastic, well balanced and very good.
I must have got the Bourns VR's pre-set reasonably well.
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The part numbers for the Bourns VR's were:

For the 10K VU meter levels adjusters:
2 x 25 Turn 10K ohm: https://www.mouser.com/ProductDetail/Bourns/3296Y-1-103LF

For the 22K EQ trimmers:
4 x 25 Turn 25K ohm: https://www.mouser.com/ProductDetail/Bourns/3296Y-1-253LF

For the 33K Playback/Balance trimmers:
4 x 25 Turn 50K ohm: https://www.mouser.com/ProductDetail/Bourns/3296Y-1-503LF

So, that's about it for the moment. I am now waiting on getting an AC RMS Millivolt meter so that I can perform the calibration and final adjustments with some accuracy. (Previously I tried to use a Multi-meter, which at 1Khz probably gave a fair Milli-volt reading around 450mV, but as I found, at higher frequencies it is less than ideal)

So until then, Cheers.
 
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Hi All,

Whilst waiting to get hold of an AC millivolt meter I thought I might have a look at a couple of other 'mechanical' adjustments. The first that comes to mind is the forward and reverse 'back tension' which plays such an important role in keeping the tape evenly pulled against the heads etc. However, looking at the instructions in the service manual, page 34, I'll be damned if I can figure out just how they have the tension gauge hooked up. The instructions say to fasten a fine string to a No. 7 Reel Hub??

Has anyone performed this adjustment?

Just how do you go about hooking up the tension gauge whilst the machine is in 'Play' mode? Is the piece of 'string' actually fixed to the reel, or is it intended to be able to 'slip'? They say to pull the tension gauge in particular directions, is the reel supposed to be able to rotate whilst this happens? or are we trying to keep the reel still against the motor?

Forgive these no doubt novice questions.

Cheers.
 
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