tnsmnichols
Active Member
As I look at all of these pics... the anticipation is building!
Yet another High serial 400 rehabilitation......
- Thread starter larryderouin
- Start date
bhamham
Super Member
Larry, looking good! That 400 should be making beautiful music before long after the maestro's touch.
You know, I think I have or one's crossed my path - a 8X,XXX serial numbered 400. I'll check when we're back in TX.
Good luck with the truck, if only they were as easy to work on as these Fisher's.
You know, I think I have or one's crossed my path - a 8X,XXX serial numbered 400. I'll check when we're back in TX.
Good luck with the truck, if only they were as easy to work on as these Fisher's.
Larry -- The laundry list of items you're attending to on this Fisher is impressive, and your work is equally so! If I may however, let me offer one point to consider:
Just as when the cathode terminals are raised above ground by the installation of 10 ohm current sampling resistors you need to "reground" the 220 ohm heater winding balancing resistors, you also need to follow the same approach with the screen grid terminals as well.
When you insert 100 ohm Screen Stability resistors at the screen grid terminals, ALL existing wiring needs to first be removed from these terminals -- just as you did at the cathode terminals to install the current sampling resistors there. But it appears that your new 1.2K 10 watt resistor is still drawing power directly from a screen grid terminal -- meaning that the power for the rest of the receiver is drawing its current through the Screen Stability resistor for that one tube, upsetting the balance of the output stage for the channel it's connected to.
The 1.2K 10 watt resistor should be connected to the new screen grid buss line, just as all the Screen Stability resistors are. That way, balance in the output stage is maintained, and the little Screen Stability resistors are ONLY handling the current of the screen grid they are connected to.
Because of other connections often requiring to be made to the screen grid buss (like the one of this discussion), this is why I always use a spare output tube socket terminal to effect the buss connections if possible, which makes for a neat installation as well. I did this with Al's X-202B that you commented on, wherein I used pin #1 of the 7591 output tube sockets as the new screen buss terminal. You might check the tubes for certain, but it appears that pin #8 could be used for this service with 7868 tubes.
Super work! I know it will be great when finished!
Dave
Just as when the cathode terminals are raised above ground by the installation of 10 ohm current sampling resistors you need to "reground" the 220 ohm heater winding balancing resistors, you also need to follow the same approach with the screen grid terminals as well.
When you insert 100 ohm Screen Stability resistors at the screen grid terminals, ALL existing wiring needs to first be removed from these terminals -- just as you did at the cathode terminals to install the current sampling resistors there. But it appears that your new 1.2K 10 watt resistor is still drawing power directly from a screen grid terminal -- meaning that the power for the rest of the receiver is drawing its current through the Screen Stability resistor for that one tube, upsetting the balance of the output stage for the channel it's connected to.
The 1.2K 10 watt resistor should be connected to the new screen grid buss line, just as all the Screen Stability resistors are. That way, balance in the output stage is maintained, and the little Screen Stability resistors are ONLY handling the current of the screen grid they are connected to.
Because of other connections often requiring to be made to the screen grid buss (like the one of this discussion), this is why I always use a spare output tube socket terminal to effect the buss connections if possible, which makes for a neat installation as well. I did this with Al's X-202B that you commented on, wherein I used pin #1 of the 7591 output tube sockets as the new screen buss terminal. You might check the tubes for certain, but it appears that pin #8 could be used for this service with 7868 tubes.
Super work! I know it will be great when finished!
Dave
Thanks Dave. Good Catch. That's one of those little details that we can all learn from. Normally I just run a piece of 12-14ga Romex for a new buss line above the tubes and attach all the screen resistors and the 1.2K (which is R-41, on the schematic, btwn C-56 and C-52D )directly to it. I changed to this setup to make it look more original. Will re-do.
This is how I normally do it, as shown in pic. This is the 1st one I ever did (back in 2011) and was later changed to a piece of Romex that had just the joints cut out of the insulation and liquid electrical tape applied to the joints.
Larry
This is how I normally do it, as shown in pic. This is the 1st one I ever did (back in 2011) and was later changed to a piece of Romex that had just the joints cut out of the insulation and liquid electrical tape applied to the joints.
Larry
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03AUG2014 1320Hrs. FINAL SOLUTION to the 1.2K 10W resistor. I'll leave it as is then. Thanks Dave for the backup.
As the 1.2K 10W resistor(R41) is between the B+ supplies for the Center Tap of the output transformers (fed off C52D) and the Screens (Fed off C56) in the power supply, rather than re wiring the whole screen resistor setup, I moved R-41 directly between C56 and C52D.
Here's a test shot before I finalize it all.
It's still electrically correct, and matches up better with the schematic. I don't think the extra heat will be a problem with the new CAN CAPS (105*C rated) once they are in. I did leave all of the lead on R41 and mounted it as high as it would go away from the other components.
Visually the output section looks less cluttered this way, and the power supply area doesn't look any worse.
COMMENTS?????????
Larry
As the 1.2K 10W resistor(R41) is between the B+ supplies for the Center Tap of the output transformers (fed off C52D) and the Screens (Fed off C56) in the power supply, rather than re wiring the whole screen resistor setup, I moved R-41 directly between C56 and C52D.
Here's a test shot before I finalize it all.
It's still electrically correct, and matches up better with the schematic. I don't think the extra heat will be a problem with the new CAN CAPS (105*C rated) once they are in. I did leave all of the lead on R41 and mounted it as high as it would go away from the other components.
Visually the output section looks less cluttered this way, and the power supply area doesn't look any worse.
COMMENTS?????????
Larry
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Looks perfect Larry -- that's a great solution to the problem as well!
Dave
Dave
Removed double post.
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The moving of R41 gave up some room to put the Balance/BIAS board right there. It's a bit different looking than the one Dave made but it's actually as the schematic is drawn. wish I had longer standoffs but the 20mm are just long enough. I had to egg out the holes a little to match the ventilation holes for mounting (don't add holes). I got two right up against the transformers in use. I added a good thick layer of Hot Glue to the bottom of the board for insulation as it's real close under there.
The wires top to bottom
LEFT SIDE (top of board)
"D" grid return
"C" grid return
B+ from Heater Supply
Right SIDE (bottom of board)
Ground wire to chassis (-)
"B" grid return
"A" grid return
Balance pots are toward the top of the board with the BIAS pots at the bottom. Test points on the tube sockets are Ring crimp connectors, where I "cupped" the rings to fit around the socket lug, then inserted the resistor wire thru the hole on both, wrapping around then soldering it all together.
This area is FINISHED NOW except for the Phase inverter resistors (1%) and adjustment.
Next up is the Bias supply (Rectumfrier and the Negative Supply).
I used a RECTRON 8A 400V tabletop rectifier bridge from Mouser. Basically the same as the Ratshack part but about 60% less cost. Mounted to side bulkhead in place of the truncated terminal strip and bridge that FISHER used. When I grabbed the old rectifier the One AC lead came apart. So much for spare parts, eh!. Removed the old Bias cap, rectifier, R34&35, C42.
Taped the 2-4700uf/50V caps, Negative leads inside, and mounted a 4 terminal strip to the caps.
Top to bottom leads + , -, -, + (1,2,3,4) Negatives(2,3) tied together.
The 15ohm 7.5W resistor and the + terminal of the rect tied together and run to #1 terminal . The resistor, +terminal and the wire lead are crimped with a ring crimp (ring cut off), then soldered with Heatshrink covering.
The heater supply, Negative Terminal of the Rect., and Supply for BAL/BIAS board connected to the NEGATIVE (2-3) terminals.
Terminal #4 run to the ground at the terminal strip where attached originally.
I reversed the caps orientation so the leads were out in the open vs. crammed up against the bulkhead, which usually isn't enough room for the rectifier and the wire joints. I think it looks a lot better this way. The exposed joints on the terminal strips can be painted with liquid electrical tape if wanted.
For right now it's not finished until it gets powered up and the actual voltages are taken and resistors added to bring the B+(or B-) down to allow the heaters to run between 11.6 and 12v. I thought I had some 1/2" 4-40 screws, but not. So the rectifier is hanging right now.
Tomorrow the Phase inverter resistors and adjustment.
If you guys see any "GAFF's" speak up. I spent all afternoon on the BIAS SUPPLY. I built the board in an hour this morning, but it was 1 when I started on the Bias Supply and finished about 5.
Larry
The wires top to bottom
LEFT SIDE (top of board)
"D" grid return
"C" grid return
B+ from Heater Supply
Right SIDE (bottom of board)
Ground wire to chassis (-)
"B" grid return
"A" grid return
Balance pots are toward the top of the board with the BIAS pots at the bottom. Test points on the tube sockets are Ring crimp connectors, where I "cupped" the rings to fit around the socket lug, then inserted the resistor wire thru the hole on both, wrapping around then soldering it all together.
This area is FINISHED NOW except for the Phase inverter resistors (1%) and adjustment.
Next up is the Bias supply (Rectumfrier and the Negative Supply).
I used a RECTRON 8A 400V tabletop rectifier bridge from Mouser. Basically the same as the Ratshack part but about 60% less cost. Mounted to side bulkhead in place of the truncated terminal strip and bridge that FISHER used. When I grabbed the old rectifier the One AC lead came apart. So much for spare parts, eh!. Removed the old Bias cap, rectifier, R34&35, C42.
Taped the 2-4700uf/50V caps, Negative leads inside, and mounted a 4 terminal strip to the caps.
Top to bottom leads + , -, -, + (1,2,3,4) Negatives(2,3) tied together.
The 15ohm 7.5W resistor and the + terminal of the rect tied together and run to #1 terminal . The resistor, +terminal and the wire lead are crimped with a ring crimp (ring cut off), then soldered with Heatshrink covering.
The heater supply, Negative Terminal of the Rect., and Supply for BAL/BIAS board connected to the NEGATIVE (2-3) terminals.
Terminal #4 run to the ground at the terminal strip where attached originally.
I reversed the caps orientation so the leads were out in the open vs. crammed up against the bulkhead, which usually isn't enough room for the rectifier and the wire joints. I think it looks a lot better this way. The exposed joints on the terminal strips can be painted with liquid electrical tape if wanted.
For right now it's not finished until it gets powered up and the actual voltages are taken and resistors added to bring the B+(or B-) down to allow the heaters to run between 11.6 and 12v. I thought I had some 1/2" 4-40 screws, but not. So the rectifier is hanging right now.
Tomorrow the Phase inverter resistors and adjustment.
If you guys see any "GAFF's" speak up. I spent all afternoon on the BIAS SUPPLY. I built the board in an hour this morning, but it was 1 when I started on the Bias Supply and finished about 5.
Larry
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Phase Inverter Resistors R101-102(390K), R103-104(1.2K), R109-110(47K),R111-112(120K) replaced with 1% resistors, and matched side to side.
Had a bit of a scare thinking FISHER had screwed up. I was reading the schematic and incorrectly identified R115-116 as R111-112. I got it figured out.
Phase Inverters were adjusted per Dave's instructions (see sticky threadhttp://www.audiokarma.org/forums/showthread.php?t=559415 ) and both sides adjusted out @ 47.0Kohms. Quick and easy.
Now about the only thing to do left is to get the CAN CAPS and finish the POWER SUPPLY Resistors, plug it in to the DBT/Variac and see what happens.
Had a bit of a scare thinking FISHER had screwed up. I was reading the schematic and incorrectly identified R115-116 as R111-112. I got it figured out.
Phase Inverters were adjusted per Dave's instructions (see sticky threadhttp://www.audiokarma.org/forums/showthread.php?t=559415 ) and both sides adjusted out @ 47.0Kohms. Quick and easy.
Now about the only thing to do left is to get the CAN CAPS and finish the POWER SUPPLY Resistors, plug it in to the DBT/Variac and see what happens.
Attachments
tnsmnichols
Active Member
Audiokarma is such a wonderful forum! I can't think of another place where such a collective wealth of knowledge exists... As someone who barely knows the difference between a resistor and a capacitor, I am VERY fortunate to benefit from the collaborative efforts of you Fisher Gurus! :ntwrthy:
The Can Interstage resistors are in. Now waiting on The Can's. talked to TOM @ Hayseed and he said they'll ship Thursday at the latest. So figure anytime after next wednesday. The only thing I have yet to do is install the can's, power it up and do final adjustments (crossing fingers, toes, and any other parts that'll help!). Oh yeah. The PAPER WORK!!! Remember the old cartoon with the kid sitting in a 2 holer straining, with the caption......"No job is finished UNTIL THE PAPER WORK IS DONE!"
Larry
Larry
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Parts are all in now.
The Can's showed up today. Installed along with the new interstage resistors, and cleaned up a couple of joints I wasn't happy with.
Tomorrow is Variac/DBT power up, check the heater voltages on V8-9-10-11 and install a resistor and cap to get them where they are supposed to be if necessary. As it had a Silicon bridge from the Factory, this may or may not be needed from a standpoint of voltage drop.
After making sure no Magic smoke is or going to be released, Balance and Bias the output's and recheck the P.I tune. It should be ok, as I checked it again today and it was dead on balanced at 47Kohms. Those 1% resistors do help. Then we get into the 96 hour engineering plant power run. If something is gonna break it's during this time, it seems. Once it passes then it's off to Toms to find a place to happily play for a lonnnngggg time.
What he wanted was a unit that was as stock as possible, but updating components and making it as safe as possible and still keeping the stock look and sound. I think I've accomplished that. Granted i used a couple of K73's in the phono and voltage amp sections, everything else is standard Nichicon, Vishay, KOA Speer, Ohmite, and Cornell Dublier parts, along with the Hayseed Hamfest Can's. Personally I think they fit the FISHER's aesthetically better than the original CE/Mallory type's.
So on to the almost last pictures of this rehabilitation.
1st up. The upper stage of the Doubler (3 section can) this is the 200/40/40 uprated to 220/47/47 @450/250/250V. The Ohmites are the 330ohm 3W (R42 & R43.
Next is the Lower stage of the Doubler (right), and the 4 section Can(Left)
with the rest of the power supply and Bias Supply thrown in. The Single Double cap is uprated from 100uf @ 250v to 220uf@450V. The 4 section is uprated from 40/40/40/20 @ 500/450/400/300 to 47/47/47/22uf @ 600/450/450/350V. The Bias caps are 4700uf 50V Nichicon's. UF 4007's, CL-80's, and X-Y cap.
The 400 overall under the skirt. The output couplers are 400V EROFOIL II (NOS from Apple Scruff). Plus all the other stuff listed in previous posts.
And finally the TOP SHOT. It needs a knob bright (Tom will handle that). And with those Hayseed Can's it looks HIBROW!
I'm gonna go scrape the Solder fumes off of me (along with the old grease from the truck. just try and change plugs and wires on an '02 S-10 without scraping and broiling your arms) I know better than working on it while it's hot, but no choice! No I didn't get burned, but it was uncomfortable there for a few minutes against the manifolds.
Gnight all.
Larry
The Can's showed up today. Installed along with the new interstage resistors, and cleaned up a couple of joints I wasn't happy with.
Tomorrow is Variac/DBT power up, check the heater voltages on V8-9-10-11 and install a resistor and cap to get them where they are supposed to be if necessary. As it had a Silicon bridge from the Factory, this may or may not be needed from a standpoint of voltage drop.
After making sure no Magic smoke is or going to be released, Balance and Bias the output's and recheck the P.I tune. It should be ok, as I checked it again today and it was dead on balanced at 47Kohms. Those 1% resistors do help. Then we get into the 96 hour engineering plant power run. If something is gonna break it's during this time, it seems. Once it passes then it's off to Toms to find a place to happily play for a lonnnngggg time.
What he wanted was a unit that was as stock as possible, but updating components and making it as safe as possible and still keeping the stock look and sound. I think I've accomplished that. Granted i used a couple of K73's in the phono and voltage amp sections, everything else is standard Nichicon, Vishay, KOA Speer, Ohmite, and Cornell Dublier parts, along with the Hayseed Hamfest Can's. Personally I think they fit the FISHER's aesthetically better than the original CE/Mallory type's.
So on to the almost last pictures of this rehabilitation.
1st up. The upper stage of the Doubler (3 section can) this is the 200/40/40 uprated to 220/47/47 @450/250/250V. The Ohmites are the 330ohm 3W (R42 & R43.
Next is the Lower stage of the Doubler (right), and the 4 section Can(Left)
with the rest of the power supply and Bias Supply thrown in. The Single Double cap is uprated from 100uf @ 250v to 220uf@450V. The 4 section is uprated from 40/40/40/20 @ 500/450/400/300 to 47/47/47/22uf @ 600/450/450/350V. The Bias caps are 4700uf 50V Nichicon's. UF 4007's, CL-80's, and X-Y cap.
The 400 overall under the skirt. The output couplers are 400V EROFOIL II (NOS from Apple Scruff). Plus all the other stuff listed in previous posts.
And finally the TOP SHOT. It needs a knob bright (Tom will handle that). And with those Hayseed Can's it looks HIBROW!
I'm gonna go scrape the Solder fumes off of me (along with the old grease from the truck. just try and change plugs and wires on an '02 S-10 without scraping and broiling your arms) I know better than working on it while it's hot, but no choice! No I didn't get burned, but it was uncomfortable there for a few minutes against the manifolds.
Gnight all.
Larry
Attachments
Very nice job, Larry! Tom is going to enjoy it for a long time for sure!
Dave
Dave
tnsmnichols
Active Member
It's beginning to feel like Christmas is here in August!
Thanks for the Kudo's. I always get skittish after doing one of these and before hitting it with power. I'm taking a break right now, working on a project for my neighbor. Hopefully I'll get it done today and can take my worries out on some 2x4's.
Larry
EDIT: All the parts removed from the 400.
Larry
EDIT: All the parts removed from the 400.
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tnsmnichols
Active Member
Thanks for the Kudo's. I always get skittish after doing one of these and before hitting it with power. I'm taking a break right now, working on a project for my neighbor. Hopefully I'll get it done today and can take my worries out on some 2x4's.
Larry
EDIT: All the parts removed from the 400.
You've got the old parts ready for the gallon ziplock! Great!:yes:
It's ALIVE!!!!
Brought it up on the Variac/DBT. Noticed the Light was bright and getting brighter as I came up. Looked down and the 1.2K 10W (R41) doing a Damned good imitation of a REDPLATING 7868.
Shut it down, removed the output's and brought it up again slowly. BULB STAYED DIM. Put in tubes one by one and when V17 in, the lamp lit and the resistor went CHERNOBYL. :worried:
Started tearing stuff out and found the culprit.:grumpy: When I added the standoff's for the Improved IBAM board, I had to undo the transformer bolts and nuts to move the transformers so I could get the screws in the holes. When I put the nuts back on, I thought I had moved the wiring to clear the nuts. Apparently not.:stupid::stupid: The wire from V16 to V17 screens got trapped and insulation cut. Backed off the nut and found the wire was ok. Insulation had a small cut,:nono: and I didn't have anymore orange wire. 2 layers of Heatshrink and all is good. The resistor tested 1,198ohms but it looked like a piece of taffy that had just been started to pull so I replaced it:thmbsp:
The 7868's are fairly worn. :cry: The balance doesn't stay put between them varying from -4 to +6mv, with the unit in aux, no source connected, all other controls centered and volume all the way down.
BIAS is showing that the tubes can be balanced @ a MAXIMUM of 28.75ma with the pot maxxed out to the stop. Bias voltage at that point is -14.36 to -14.73 Going the other way ma's are around 18 to 20ma with a voltage of approx -20v.
INPUT VOLTAGE 117VAC by VARIAC.
Bias /Heater B- is -25.2v at the caps which is verified by -12.6 @ the heaters. (Dave; Do you think a resistor and cap in the heater circuit is warranted here?)
V17 voltages (V14,15,16 are same except as noted below)
Pin1 348VDC
Pin2 -14.65VDC
Pin3 27.94 to 28.02mv DC or 279.4 to 280.2 ma 10.61W
Pin4 3.05 (AC HTR)
Pin5 3.15 (AC HTR)
Pin6 See Pin2
Pin7 See Pin1
Pin8--------
Pin9 378VDC
V16
Pin 2 -14.36vDC
Pin 3 27.80 to 28.02mv 278.0 to 280.2ma 10.64W
V15
Pin 2 -14.73vDC
Pin 3 27.91 to 28.20mv 279.1 to 282.0ma 10.66W
V14
Pin 2 -14.38vDC
Pin 3 27.91 to 28.02mv 279.1 to280.2ma 10.65W
This is telling me that these tubes although servicable, are near end of life.
Transformers after an hour are lukewarm to warm. (about 100-110) Can caps are ambient temp or slightly warmer due to radiant heat from adjacent tubes or transformers.
The tuner on this one is rock solid and appears to be in alignment. Most of the time with these and the 800's I've seen, they've tuned visually off center, either by the tuning tube or the meter. but this one pretty well dead center. It picks up the one station I have trouble with even with a newly aligned tuner. And it's strong, with no ghosting or bleedover from the adjacent stations @100.3 and 101.1. This is inside the RV and a dipole inside. RV is all metal, no Fiberglass. So for this to get over 1/2 bars on the EM84 is outstanding. MPX is also outstanding. Best separation I've heard in a long time. It actually sounds pretty good with the output tubes in it. But it will probably sound a bit better with new tubes in it.
I'm gonna run it for 96 to 100 hours and TOM can try and get it outta my hands.:zoom:
Now to button it up and do the burn in.
CUT......PRINT IT. It's a WRAP!!!
Larry
Brought it up on the Variac/DBT. Noticed the Light was bright and getting brighter as I came up. Looked down and the 1.2K 10W (R41) doing a Damned good imitation of a REDPLATING 7868.
Shut it down, removed the output's and brought it up again slowly. BULB STAYED DIM. Put in tubes one by one and when V17 in, the lamp lit and the resistor went CHERNOBYL. :worried: Started tearing stuff out and found the culprit.:grumpy: When I added the standoff's for the Improved IBAM board, I had to undo the transformer bolts and nuts to move the transformers so I could get the screws in the holes. When I put the nuts back on, I thought I had moved the wiring to clear the nuts. Apparently not.:stupid::stupid: The wire from V16 to V17 screens got trapped and insulation cut. Backed off the nut and found the wire was ok. Insulation had a small cut,:nono: and I didn't have anymore orange wire. 2 layers of Heatshrink and all is good. The resistor tested 1,198ohms but it looked like a piece of taffy that had just been started to pull so I replaced it:thmbsp:
The 7868's are fairly worn. :cry: The balance doesn't stay put between them varying from -4 to +6mv, with the unit in aux, no source connected, all other controls centered and volume all the way down.
BIAS is showing that the tubes can be balanced @ a MAXIMUM of 28.75ma with the pot maxxed out to the stop. Bias voltage at that point is -14.36 to -14.73 Going the other way ma's are around 18 to 20ma with a voltage of approx -20v.
INPUT VOLTAGE 117VAC by VARIAC.
Bias /Heater B- is -25.2v at the caps which is verified by -12.6 @ the heaters. (Dave; Do you think a resistor and cap in the heater circuit is warranted here?)
V17 voltages (V14,15,16 are same except as noted below)
Pin1 348VDC
Pin2 -14.65VDC
Pin3 27.94 to 28.02mv DC or 279.4 to 280.2 ma 10.61W
Pin4 3.05 (AC HTR)
Pin5 3.15 (AC HTR)
Pin6 See Pin2
Pin7 See Pin1
Pin8--------
Pin9 378VDC
V16
Pin 2 -14.36vDC
Pin 3 27.80 to 28.02mv 278.0 to 280.2ma 10.64W
V15
Pin 2 -14.73vDC
Pin 3 27.91 to 28.20mv 279.1 to 282.0ma 10.66W
V14
Pin 2 -14.38vDC
Pin 3 27.91 to 28.02mv 279.1 to280.2ma 10.65W
This is telling me that these tubes although servicable, are near end of life.
Transformers after an hour are lukewarm to warm. (about 100-110) Can caps are ambient temp or slightly warmer due to radiant heat from adjacent tubes or transformers.
The tuner on this one is rock solid and appears to be in alignment. Most of the time with these and the 800's I've seen, they've tuned visually off center, either by the tuning tube or the meter. but this one pretty well dead center. It picks up the one station I have trouble with even with a newly aligned tuner. And it's strong, with no ghosting or bleedover from the adjacent stations @100.3 and 101.1. This is inside the RV and a dipole inside. RV is all metal, no Fiberglass. So for this to get over 1/2 bars on the EM84 is outstanding. MPX is also outstanding. Best separation I've heard in a long time. It actually sounds pretty good with the output tubes in it. But it will probably sound a bit better with new tubes in it.
I'm gonna run it for 96 to 100 hours and TOM can try and get it outta my hands.
:zoom:Now to button it up and do the burn in.
CUT......PRINT IT. It's a WRAP!!!
Larry
Hi Larry -- Nice job. the B+ voltages are lower than I'm used to, but with the control grids only requiring about -14.5 vdc, it would certainly suggest that the tubes are well worn. Even your heater voltage is low. I assume you've got a CL installed, so with that, and only 117 vac at the plug, that is likely the reason you can't get any more current draw out of the output tubes. You might try plugging the unit straight into your wall power and see how it does that way.
Multi-turn pots would no doubt be a nice upgrade. I used the single turn due to the installation I used on my 800C. I will investigate the idea of using multi-turn pots in the future.
Nice job!
Dave
Multi-turn pots would no doubt be a nice upgrade. I used the single turn due to the installation I used on my 800C. I will investigate the idea of using multi-turn pots in the future.
Nice job!
Dave
tnsmnichols
Active Member
Sounds like I better start saving my pennies for a set of 7868's. Would love to find an old set that test strong... but will probably end up getting a matched quad of EH's from McShane... although, I have to stay I'm a little wary of the "fat pin" issue.
It will be interesting to see how long this original set will last...
"...96-100 hours..." This is torture, plain and simple!
It will be interesting to see how long this original set will last...
"...96-100 hours..." This is torture, plain and simple!
The 117VAC was on the connections of the Cl's downstream, not the upstream CL power cord connection. In the trailer I had 112-113 at the plug, that's why i put the variac inline to run it up a little. Tweaked the Variac so i was getting 117 AFTER the CL's.
I agree the B+ voltages are a little low. When I bring it in the house tomorrow, I'll recheck them with and without the variac. The heater voltages on pins 4 & 5 were taken individually with respect to chassis ground. I get 6.27vac across pins 4 & 5.
All the B+ leads from the caps are consistantly low. I'm thinking the input voltage in the trailer is low due to it has to go thru a Magnetek power center (fuse panel, and DC Inverter, with charger) then out to the branches. I had the roof mount A/C unit on FAN only and was getting 110 at the wall. took it off line and it came up 3 volts. Looks like i have some cleaning of contacts, buss bar connections, etc. in the future.
When I took the Wall voltage up to 120v the B+ at pin 9 only climbed to 390v with the screens going up to 356V.
Wish I still had my 400 with the EH7868's in it. Someday maybe again.
I agree the B+ voltages are a little low. When I bring it in the house tomorrow, I'll recheck them with and without the variac. The heater voltages on pins 4 & 5 were taken individually with respect to chassis ground. I get 6.27vac across pins 4 & 5.
All the B+ leads from the caps are consistantly low. I'm thinking the input voltage in the trailer is low due to it has to go thru a Magnetek power center (fuse panel, and DC Inverter, with charger) then out to the branches. I had the roof mount A/C unit on FAN only and was getting 110 at the wall. took it off line and it came up 3 volts. Looks like i have some cleaning of contacts, buss bar connections, etc. in the future.
When I took the Wall voltage up to 120v the B+ at pin 9 only climbed to 390v with the screens going up to 356V.
Wish I still had my 400 with the EH7868's in it. Someday maybe again.
