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Thanx everyone for your suggestions in trying to help with getting the amp running. While no one gave the exact solution I would like to think that with your help and suggestions I stayed on the issue long enough to figure it out. So, without further ado , here is the problem, and no snickering please...
What was the problem? When I rebuilt the amp to RH configuration I kept part of the power supply to the driver tube from the previous configuration. But to get it to the new driver tube anode voltage I needed to have 100k dropping resistors to the 12ax7 plates. And foolishly instead of running the 100k to the 12ax7 anode I put them from the B+ tap to the film cap supply, and then I wired it to the anodes. I went back and put the 100k resistors from the film cap B+ to the 12ax7 anodes and Voila, it works and sounds great to boot. Thanx again everyone, Happy Holidays, Dak
Follow Ups:
You do not mention your impressions of the amp now that it is working.From the schematics attached in the other thread, it seems you were building the "original" RH Universal, where the feedback resistor is at the same time the anode resistor of the driver tube?
In that case, the schematics requires an ECC81 (12AT7), otherwise it is going to work, but far from optimal.
Your solution mentions a separate anode resistor of 100k, thus it seems you have built the RH Universal v2. This one is supposed to be totally universal, but for 12AX7 (ECC83) you should use both 100k resistors in series, i.e. 200k (Rfb)... otherwise it is very much sub-optimal.
So, which one did you build, and what are your impressions?
******
http://rh-amps.blogspot.com/
Edits: 12/20/14
Just wanted to pop in and say hello.
I am currently listening to the 3rd or 4th RH84 I have built. (Early version with SS Rectification)
There is probably over 2500 hours on this current amp alone.
Myself and everyone who has heard it thinks it sounds great.
Thanks.
Happy Holidays.
Garg0yle, thank you for popping in and sharing your opinion with us. I am glad that you're enjoying the RH84.
DAK: there should be no hum whatsoever, after all this is an indirectly heated tubes amp. I understand you have built the v2, so you have both 100k anode and 200k Rfb.
If you are having hum issues, they are either power supply related (ripple too high: what is the schematics of your power supply?) or induced by radiation or grounding issues (the latter a relatively common problem with modified amplifiers - due to imperfect soldering or similar). Mine is totally hum-less (perfectly silent).
Interestingly enough, usually correcting the hum will also improve sound clarity and overall quality, so it is a win-win goal.
Let us know.
******
http://rh-amps.blogspot.com/
Hi Alex, I am using a 12ax7 driver tube and installed a 200k anode to anode resistor. The amps sounds very good except for some hum. I first rebuilt the amp in the stock configuration and there was just a trace of hum. I simply converted the amp to your design and while the hum is just audible when your ear is close to the speakers ( 91 dB efficiency ), I am wondering why there is more hum.
Another thing I noticed is that the gain in the amp is much more than before. I wonder if the increased gain, almost twice as much, has made the hum also more audible. So, I am thinking if for the 12ax7 and 7591 combination if more feedback in the anode to anode resistor of the 12ax7 to the 7591 is needed. Also do you think I need to adjust the bias resistor on the 12ax7? Your suggestions are most welcomed.
Edits: 12/20/14
So, you blocked DC voltage to the anodes? But, didn't that show in your voltage readings? I thought they were ok?
I know, the voltages were still there. But the signal was not being passed. Where was it going? I dunno. I guess the signal must have been going into the big film cap. regards, Dak
Edits: 12/11/14
What'd I tell ya? look for subtleties in the assembly.
Don't feel bad though. Troubleshooting something that has never worked is usually harder than troubleshooting something that used to work just fine.
The signal on the plate was eaten by the cap. More common mistake is using a bypass cap on a cathode follower bias resistor. It is fun when these problems get fixed and the silence is replaced by music.
It was funny, I told my boss at work that I had this amp that was not working and he told me he had a hammer that might fix it. I told him I had 3 hammers and then he said he had a bigger sledge hammer. And then he asked if I was going home and I told him no I was going to work on the amp. And the next thing I did was look at the driver tube power supply and I realized that I had wired it incorrectly. I then rewired it, and presto, bingo, shazam.... it works and sounds great. thanx for the support. Dak
What gives? Well it's fixed anyway.
Lounge Audio LCR MKIII
http://www.newrecordday.com/lounge-audio-mkiii-lcr-phono-preamplifier/
Edits: 12/11/14
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