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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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 Post subject: Re: Pimp my tube amp
PostPosted: 13 Sep 2012, 08:10 
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Spent a delightful afternoon with retro-34UL. And I thought it "funny" that sometimes we 'tend to overlook some of the more common types of tubes and chase down the weird and strange to say "hey look what I did with this". Tubes like the EL34 and EL84, KT88 and 6V6. All delightfully lovely tubes but not always incorporated in modern builds by those seeking new thrills. Yes these are readily available pentodes. There is some easily obtainable and delightfully sounding triodes too: 300B, 2A3,6AS7 and 45s.

Matt has, what looks like, a very nice 6V6 amp. Why didn't he select some hard to get, left of center, tube for his build. He speaks glowingly of the 6V6 sound and how the amp gives him just what he wants. I guess I coming over all gushing because this very simple EL34 amp I just built sounds remarkable (excuse the pun). Talking to other tube-a-holics, the Svetlanas I was given are meant to be amongst the finest examples of this tube type.

I have some rare NOS Siemens EL34s which I have listen to before (not in this amp) which I think may top the Svetlanas At this point I'm just enjoying the ultimate music simplicity of tube and amp synergy. Don't overlook the common tubes, they are a proven product.

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 Post subject: Re: Pimp my tube amp
PostPosted: 14 Sep 2012, 23:25 
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Some better shots of the amp with retro-thermionic decal. Also an under the bonnet shot. This amp has no bottom plate.
Attachment:
retro-34UL_I.jpg
Attachment:
retro-34UL_II.jpg
Attachment:
UnderBonnet.jpg


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 Post subject: Re: Pimp my tube amp
PostPosted: 15 Sep 2012, 07:41 
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I was a surprised to see how much gain this amp had.100mV in produced 20pp out. To me that is a gain of 46db. Have I got this wrong?

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 Post subject: Re: Pimp my tube amp
PostPosted: 15 Sep 2012, 10:08 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Mark, correct for voltage gain. If that is re 8 ohms then the power output is about 6.5 watts. A good value for anEL34 in SE mode. I'm with you and would expect less gain . There must be a significant voltage gain in the output stage. The winding ratios in the output transformer will also have a play in voltage gain. The two tube configuration has been used in many amps in the past and without nfb to control or limit the gain the values would be similar to yours.

I like the blue top mounting plate. Chrome transformer covers would be killers on it. :)

Good listening
Bruce

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 Post subject: Re: Pimp my tube amp
PostPosted: 15 Sep 2012, 18:51 
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@Bruce I wanted this amp to be salable and appeal to a wide audience. I thought if I painted the top plate anything but black it will never sell. But when I thought of the big black iron atop I felt it would contrast well and compliment a blue top plate. Therefore the colour. When I did Luciano (807) I got one negative comment about too much colour. In real life it looks much better than in the photo. So I'm afraid chrome bells for the trannies may have been just too ostentatious. Thanks for the nice comment and suggestion. I strive for form and function.

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 Post subject: Re: Pimp my tube amp
PostPosted: 16 Sep 2012, 00:41 
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Attachment:
retroPS.jpg
The updated schematics
Attachment:
retroamp.jpg


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 Post subject: Re: Pimp my tube amp
PostPosted: 17 Sep 2012, 03:34 
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I took the retro-34UL to a friend's (Dave) place to play on his $26K 6' high speakers. They are 92db efficient and the amp had no problem producing good volume. Dave picked straight away that the bottom end was a bit light. The amps starts to roll off at about 50hz. He did love the sound and thought it as good as his $5K 845 SEs just missing the deep bass they can produce.

I brought the amp home and tried upgrading the coupling cap from 0.22uf to 0.32uf. I knew the cheap 15W Edcors were responsible but I thought I'd give it a go. No luck the low frequencies roll-off still is after 50hz. at 40hz bass is down by at least 6db. Amp still sounds nice though. The next build will have the better Edcors. I'm using the 15W GSX which Edcor will go down to 70Hz. They are better than that at lower power (e.g.5W). The GXSE15-8-5K would be far better.

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 Post subject: Re: Pimp my tube amp
PostPosted: 17 Sep 2012, 08:50 
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I have been saying I used a 20H 200mA Hammond choke. That is incorrect the choke is a 10H 200mA Hammond 193J. I will update the PS schematic.

I'm going to start an EL34 thread. For the next builds I will be using better OPTs. I just ordered 6 of these for the next EL34 amp:https://www.edcorusa.com/p/513/gxse10-6-5k

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 Post subject: Re: Pimp my tube amp
PostPosted: 31 Oct 2012, 06:01 
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Joined: 29 May 2011, 12:24
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Location: Netherlands
Excellent thread!

Mark, is that a GZ34 rectifier you're using? When you wanted lower voltage, have you considered using a 5U4 instead (if the power transformer can take the extra current)? Or did you have a specific reason to stick to the GZ34 (less sag?) ?


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 Post subject: Re: Pimp my tube amp
PostPosted: 24 Jan 2013, 22:28 
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Joined: 24 Jan 2013, 17:24
Posts: 2
Location: Glen Burnie, MD (USA)
Hey all. I'm new to this forum, but not new to amp building. I'm looking to build an EL34 SET amp and found this forum and particularly this thread. I'm hoping to get your input on some thoughts I have.
Have you tried a 6N2P-EV in place of the 1P?
I want to use the amp in this thread as a starting point, but then add an additional 6N1P(2P) and using both halves in an SRPP arrangement for each channel? (Minimal cost increase/minimal parts increase/likely that there is enough current available with the existing iron/ and more gain -- likely a preamp wouldn't be necessary with a decent source)

Your thoughts would be greatly appreciated.

Regards,
Steve

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