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Hi, I am getting ready to ohm out the two boards and do I use J4 pins 3-5 as my ground and it says to remove J4-8 before power up, is that also with the resistance checks, and I am using a S6L7 instead of a 12AX7, do the values change for the resistance and voltage checks. One last thing RX53 and CX21 across the output terminals are they permenent fixtures. Thanks, Jim
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Hi Jim,

HOGHEAD wrote:Hi, I am getting ready to ohm out the two boards and do I use J4 pins 3-5 as my ground...

Correct.

HOGHEAD wrote:...and it says to remove J4-8 before power up, is that also with the resistance checks,...

You can leave it hooked up for resistance checks. Leaving the output transformer power disconnected when powering up for the first time is a good first step as miswirings in the output are common place problems.

HOGHEAD wrote:...and I am using a 6SL7 instead of a 12AX7, do the values change for the resistance and voltage checks.

Kind of. The pin numbering is different, of course. Did you change the orientation of the jumpers from 'Z to 4' and 'Y to 5'?

HOGHEAD wrote:One last thing RX53 and CX21 across the output terminals are they permenent fixtures. Thanks, Jim

Yes. This network provides a good load when operating into a difficult load with lots of inductance (ie some types of speakers). It's for high frequency stability outside the audio spectrum.

Shannon

Hi, yes I did add the jumpers from y to 5 and z to 4 but I am unsure of some of the readings, pins 1,2,and 3 read ok but pins 4 and 5 I get about 45k and 25k ohms and pin 6 I get 1k and pin 7 I get 50 omhs and finally on pin 8 I get 50 omhs. this is on V1-6LS7. All the other sockets and plugs seem to be ok. Jim
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HOGHEAD wrote:Hi, yes I did add the jumpers from y to 5 and z to 4 but I am unsure of some of the readings, pins 1,2,and 3 read ok but pins 4 and 5 I get about 45k and 25k ohms and pin 6 I get 1k and pin 7 I get 50 omhs and finally on pin 8 I get 50 omhs. this is on V1-6LS7. All the other sockets and plugs seem to be ok. Jim

Hi Hoghead,

1 - high Z
2 - high Z
3 - high Z
4 - Should be around 480K, ie the resistance of the the grid stopper and grid resistor to ground. Probe around and double check those resistor values. I see I have 23K on my resistance sheet for the 12AX7 grid - this is an error. I apparently had my signal source loading the input. Yellow_Light_Colorz_PDT_05
5 - This should be at least 100K. Double check the resistor values here, too - particularly R5. On my meter it starts drifting higher as this is connected to the last filtering cap in parallel with the 470K load resistor.
6 - 1.1K - double check the value of R4
7 - 50 ohms
8 - 50 ohms

So take a closer look at 4, 5 & 6.


Shannon

Shannon, I am using a Simson 260 meter and I thought I was on a 1K scale not the 10k scale so my readings on pin 4 and 5 should of been ten times higher than previously posted (operator error!) so I get 450k on pin 4 and about 250k on pin 5. Jim
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HOGHEAD wrote:Shannon, I am using a Simson 260 meter and I thought I was on a 1K scale not the 10k scale so my readings on pin 4 and 5 should of been ten times higher than previously posted (operator error!) so I get 450k on pin 4 and about 250k on pin 5. Jim

Sounds good!

Shannon

Shannon, I have started my power up checks, on one unit the voltages seem ok then I hear what sound like a high pich runaway so I shut it off, I do not have the center tap (red/yel) switched or fused (should I?) and on the other unit it blows fuses ( I had the center tap and one other lead reversed, j4-5,6) but it blows fuse until I remove the lead off j4-7, any thoughts? I have compared resistances and checked diodes d1,2,3 and I dont believe the transformer is shorted (40-80 ohms on center tap and secondaries respectfully) I know I am missing something or blew something but reversing j4-5,6 maybe. Jim
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HOGHEAD wrote:Shannon, I have started my power up checks, on one unit the voltages seem ok then I hear what sound like a high pich runaway so I shut it off, I do not have the center tap (red/yel) switched or fused (should I?)

Hi Hoghead,

Go ahead and disconnect the other output connections from the PCB. I really don't see how the remaining output primary connections could cause a problem, but the feedback connection at J1-3 could be floating in a weird spot causing problems for the 6SL7 (ie oscillation). But did you even have any tubes in it? Load or short the input RCA, too.

HOGHEAD wrote:...and on the other unit it blows fuses ( I had the center tap and one other lead reversed, j4-5,6) but it blows fuse until I remove the lead off j4-7, any thoughts? I have compared resistances and checked diodes d1,2,3 and I dont believe the transformer is shorted (40-80 ohms on center tap and secondaries respectfully) I know I am missing something or blew something but reversing j4-5,6 maybe. Jim

I think your transformer is fine - they are pretty forgiving creatures. Sounds like D1 is toast - not unexpected when swapping the leads around. I would just replace both D1 and D2 and try again.

Shannon

Shannon, I got the first one up and running, I will continue with the voltage checks and bias adjustments (about 660mv right now with KT90's)
I will let you know on the second amp, Jim
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Shannon

Shannon, still having a problem with the one amp blowing the fuse and I did replace D1 and it wont blow with J4-7 removed so I am not sure what I am missing, also what bias voltage do you think for KT90's, there are at 200mv right now. Thanks, Jim
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HOGHEAD wrote:Shannon, still having a problem with the one amp blowing the fuse and I did replace D1 and it wont blow with J4-7 removed so I am not sure what I am missing, also what bias voltage do you think for KT90's, there are at 200mv right now. Thanks, Jim

Hi Hoghead,

I run KT90's at 65mA in my Ikes. Of course, I wouldn't bias these up until you get the other half of the secondary rectifying.

Can you bias at around 30mA each (ie 300mV) and take various voltage checks in this half-wave state? Thinking...

Shannon

Shannon, thanks for the bias info, I will adjust the one thats up and running at about 65ma, (what voltage does that turn out to be at TP1 and TP2?) as I put in a couple of chassis mount test points for that and one for the ground. And any more thougt on the main fuse blowing when I attach J4-7?Thanks, Jim
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HOGHEAD wrote:Shannon, thanks for the bias info, I will adjust the one thats up and running at about 65ma, (what voltage does that turn out to be at TP1 and TP2?) as I put in a couple of chassis mount test points for that and one for the ground. And any more thougt on the main fuse blowing when I attach J4-7?Thanks, Jim

Hi Jim,

I would replace all three diodes for a sanity check. Are you using 1N4007 types? I think your transformer is fine.

Shannon

Shannon, I replaced diodes D1,D2 and D3 and that did the trick! So I have both up and running and they sound great! I dont think I would ever go back to solid state again! The bottom end comes through with authority and the top end is smooth and silky and I am hearing little things I never heard before. And just the overall impact is, well incredible.
On the bias side they are at 200mv at idle and you were saying about 65ma, that would be 650mv would it not across the bias resistors? Please let me know on the voltage. And thank you very much for all your help and patience with me. Sincerly, Jim Scivally
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