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PostPosted: 12 Jan 2010, 21:18 
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Joined: 02 Sep 2008, 14:34
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Location: Rochester, NY
Bluesman wrote:
Sorry to not be contributing to this thread lately. I am so busy with other things I simply have not had time. There are now another 15 or so potential builders who purchased pcbs and hopefully will join the forum and post their experiences here. And I wanted this to be a "collaborative effort" thread for everyone to use in hopes of helping all who are interested.
Greg,

15 more buyers, that is great!!

Is there any chance we could get an update to the Parts List on Page 1. My questions relate to the differences between the documentation and PCB, and what choices were made. Since I am one of the moderators here, I would be happy to do the edits if someone cares to send me the updates. I have a big mouser order that is almost ready to go but I want to get the UniAmp basics added to it. I do plan on using some boutique parts but there are definitely some generic pieces that I can get from Mouser.

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PostPosted: 20 Jan 2010, 19:55 
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Alan,

I'm not aware of anything that is in need of change on the parts list. Did you see something there or elsewhere that seems to be incorrect?

Cheers,
Greg


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PostPosted: 23 Jan 2010, 17:04 
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Hello all. New member of the forum but not new to playing around with diy tube amps. I am building a pair of the uniamp boards right now. I believe what some builders were confused about was the difference in some resistor ratings on the schematic vs the pc board itself - for example 1W resitors in the schematic vs 5W resistors on the pc labeling at the 6SN7 plates.
Mikey


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PostPosted: 06 Mar 2010, 16:50 
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Joined: 19 Feb 2010, 16:09
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I hope someone can help me. I have the boards finished and wired to a audionote 6.6K output transformers 350-0-350v power transformer. When I start the amp it is working but there is a slow oscillation of the speaker cone with the B+ making the same oscillation. If I pull the driver 6sn7 the amp stops oscillation and the B+ voltage is 362v and no oscillation.. The amps will work but I am afraid that it will damage a real set of speakers. What would cause this type of instability or oscillation. What can I do to fix it. It is also wired in triode and have tried it with 6L6 and EL34's. Does it need some negative feedback??? :| :| :|


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PostPosted: 07 Mar 2010, 02:49 
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I've seen that too. My Stealth 6 behaves in the same way - but only one channel.

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PostPosted: 07 Mar 2010, 20:01 
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If you can see it, it is low freq. It should not be a problem with the circuit as many have built this design. Check for errors on the board and connections. What did you use for the phase splitter transformer and is it grounded?

More questions - is it in both channels? If you disconnect the source, does it still occur? Have you tried a different source, different tubes?

I see it is your first post, so welcome to the forum.

Cheers, Gio

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PostPosted: 08 Mar 2010, 17:29 
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Finally figured it out. I was about to rebuild two eico HF-51 turning them into hf-60's. I looked at there driver section and it had the same 6sn7 driver stage. It had a 18k cathode resistor for the sharing of the two triode sections. First I tried a 15k which I had in the junk box and no oscillation. I finally used a 3.3K which I had from the junk box and voila no oscillation. I have over 25 6sn7 and none of them worked in the driver position with the original resistor. So maybe change R9 to 3.3k . the 6sn7 must be a little to stressed with the 1K. Now onto a GM-70 single ended amp I am working on and rebuilding the eico hf-51's. 8-) 8-) 8-)


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PostPosted: 09 Mar 2010, 03:38 
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GM70???!!! :eek: :o :hot: Have you written your will? ;)

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PostPosted: 15 Mar 2010, 15:00 
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Joined: 04 Oct 2008, 11:29
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Location: Chillicothe, Ohio
Thanks for posting the results of your troubleshooting. That's the whole intent of a build thread in my mind.

I'm sure this info will help others among us. I know I need all the help I can get.

Cheers,
Greg


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PostPosted: 25 Mar 2010, 18:33 
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Joined: 22 Mar 2010, 20:27
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Hello everybody,
I have just joined this group. I am wondering if the boards are still avaliable for this amp, and what the estimated cost would be to complete one. I have thoughts of putting two units on one chassis for a stereo setup.

I know I'm going to build an amp, but with the choices on just this forum alone, sheesh, I can't make up my mind.

Thanks,
Gary


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