| hacknet |
i`ve been think about building a tube power amp lately, i`ve decided on a 6L6 since i`m looking for punch bass and nice mids (for me to further apreciate dire straits and eddie van halen)
i`ve seen alot of circuits for the 6L6 but most of them being designed for guitar use.
whats a good circuit you guys recommend? i`m hoping for about 20watts.
Thanks in advance |
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| hacknet |
any other?
how much can i hope to get out of a pair of 6L6 i push pull? |
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| hacknet |
| i looked around for williamson amps and found them to use only 6550 or EL34s. are you refering to the other acrosound amps? |
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| SY |
| quote: | Originally posted by hacknet
any other?
how much can i hope to get out of a pair of 6L6 i push pull? |
Depends on the output configuration. I don't have my RCA tube manual at hand, but I think you could get 40-50W in pentode. If someone else doesn't chime in with the number, I'll find it sometime today.
A Williamson with 6L6s and a 6600 ohm plate-plate output transformer would make a very nice 18 watt triode amp. |
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| hacknet |
hmm.. looks good.
i`m new to building tube amps and i`m going to ask a silly question.
can i add a triode to UL switch since i really haven`t made up my mind which i prefer? |
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| SY |
You can, but think VERY carefully about insulation requirements in the event of switch failure and the stray reactances in wiring it up. I'd recommend doing it as a hardwired option, moving a wire or a jumper on a terminal strip. You can't do a rapid A-B test, but you can still change it over in a few minutes and you avoid a lot of complication.
:att'n:If you're new to the tube thing (and even if you're not!), do think about safety when probing around an amp that's been switched on in the recent past- capacitors can hold a lethal charge for hours after the unit is switched off. |
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| hacknet |
yup, i`ve gotten a good kick from charged caps from building previous tube gear.
btw, i cant seem to find the circuit you are talking about. PLease PLease Please point me there....
Thank You! |
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| EC8010 |
| quote: | Originally posted by hacknet
Any other? |
Yup. Use another Williamson for the other channel. |
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| SY |
| The original Williamson circuit was published in Wireless World. Quite a few variations were published in Audio Engineering and Audio- several are available reprinted in the Audio Anthology series. I haven't seen Morgan Jones's book yet, but I'll bet it's in there, too. |
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| Peter Menting |
Sy; Yes it is, 6Sn7-6sn7-KT66 (Triode Rigged)-15WPC. (Pgs 220-221)
Regards
Pete |
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| Sch3mat1c |
| quote: | Originally posted by SY
Williamson. |
Until you add NFB around a crappy OPT. Ask me about motorboating and 100kHz power oscillators, I dare you. :rolleyes:
Tim |
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| EC8010 |
| The output transformer as designed and specified by Williamson was superb. The questionable LF stability was mainly due to an oversight on Williamson's part (he couldn't be perfect everywhere). David Hafler fixed the LF problem by increasing the value of the coupling capacitors to the output valves. |
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| andyjevans |
| If you look at the thread on Leak Stereo 20 there should be my circuit for EL84s. I also use this identical circuit for 6L6 in UL PP on a pair of Leak TL25 chassis, except I'm currently using a 500 ohm cathode resistor on each 6L6 which is loafing along, but I have a small room. It's a simple circuit with few parts and it sounds very nice. This will get you going with very little effort. SY's comments about safety are, as always, worth reading carefully. |
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| SY |
Andy, IIRC, the TL25 was a Williamson but with a pentode input?
What are you getting for power out of that? |
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| andyjevans |
Andy, IIRC, the TL25 was a Williamson but with a pentode input?
What are you getting for power out of that?>
Hi there SY - Well, this pair of monobloks started off as rusty chassis with no transformers so the TL25 is rather nominal, although they do look quite nice now. I used a 6.6KOPT from Danbury with the beefy core (ex-Maplin part) which is quite good. I have about 20v on the grids of the 6L6s and 500 ohms cathode resistor so about 40mA. Loafing along. Sounded nice so I didn't carry on changing values. My idea was to use a quad of 7519, which I have ready. I got sidetracked into testing out loads of 6J5s and 6C5s in the front end, which has been good fun. Nice tubes in the archives of the 6J5, and much cheaper than 1940s 6SN7s for sure - plus you get the round plates if you like. Just listening to some Brimar ST shape 6J5 round plates as we speak. Nice! That old '40s smooth silky sound. Before those I was groovin' to some RCA metal 6C5s - surprisingly nice too. I've gone single triode for the front end - these old tubes are just too much fun. |
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| hacknet |
| quote: | Originally posted by SY
The original Williamson circuit was published in Wireless World. Quite a few variations were published in Audio Engineering and Audio- several are available reprinted in the Audio Anthology series. I haven't seen Morgan Jones's book yet, but I'll bet it's in there, too. |
oh. thats why. i don`t have one of those books lying aroun....:bawling: |
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| hacknet |
Yup. i did a wireless world search and got that too. Thanks!
i`ve found the original issue. Wireless World issue |
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| hacknet |
| one question, i recall EC8010 saying that David Hafler solve some oscillation problems by increasing the coupling capcacitors. the original issue uses a 0.25uf cap and the "revised" a 0.22uf. could i be a smart **** by putting 0.47uf? |
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| EC8010 |
| I've been searching desperately to find the article (I think it was Hafler), but I just can't seem to find it I have a feeling that the coupling capacitors were made quite a bit bigger, perhaps 1.5uF. |
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| SY |
| quote: | Originally posted by EC8010
I've been searching desperately to find the article (I think it was Hafler), but I just can't seem to find it I have a feeling that the coupling capacitors were made quite a bit bigger, perhaps 1.5uF. |
Hafler and Keroes, Audio Engineering, reprinted in Audio Anthology v2, "Ultra-Linear Operation of the Williamson Amplifier".
| quote: | from Hafler and Keroes
The low frequency time constants of the original circuit's interstage coupling networks were the same for both such networks. This is not particularly desirable in a feedback amplifier... Increasing one pair of coupling capacitors from 0.05uF to 0.25uF... increases the low frequency stability margin at nominal increase in cost. |
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| EC8010 |
| SY: Thank you for that. I "knew" it was a factor of 5:1, hence my guess at 1.5uF! |
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| analog_sa |
Hacknet
Andy's suggested circuit is much better than a Williamson. That is if you want to build a modern sounding amp and not just something of historical value.
Going as far back as the sixties amp builders noticed the Williamson plays better in mono than stereo. Lots of NFB keeps the sound strictly in the speakers, kills dynamics and soundstaging and together with the excessively repetitive use of 6SN7 produces cold and boring (for a tube amp) mids. |
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| fdegrove |
Hi,
| quote: | | Lots of NFB keeps the sound strictly in the speakers, kills dynamics and soundstaging and together with the excessively repetitive use of 6SN7 produces cold and boring (for a tube amp) mids. |
As an example:
I have a PP 2A3 amp that uses only local FB, no global loop whatsoever...
The soundstage that little amp can throw is little short of amazing.
With any decent recording you can plunk the speakers down, even only 4-5 foot apart, you just can't tell the sound comes from those speakers.
That's not to say the amp is perfect, it isn't.
For what it cost me however it's a joy to listen to.
Cheers,;) |
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| arnoldc |
| quote: | Originally posted by fdegrove
[B]I have a PP 2A3 amp that uses only local FB, no global loop whatsoever...
The soundstage that little amp can throw is little short of amazing.
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Hi Frank, i've been wanting to make a PP 2A3 and been contemplating on the JE Labs PP 2A3. However, I want to try one of yours. Is that at all possible? Share the schematic or is this a commercial amp? |
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| hacknet |
hmm... williamson or not williamson...
i`ll have a look and see what i decide on... the rest look quite game on a williamson. |
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| andyjevans |
That's not to say the amp is perfect, it isn't. For what it cost me however it's a joy to listen to.>
That's exactly my response to taking off the global feedback loop - joy! The sound just makes you like it - happy pills. Haven't got a clue how this effect measures, but I was just grinning when I heard the sound without feedback. If I'm reading the language correctly, others seem to have a similar response. Not to say that others don't grin when they add feedback - I'm sure this happens too. |
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| hacknet |
| what trans did you guys use? i`m considering a tamura or a custom winder. |
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| SY |
| Personally, I prefer vintage iron. 6600 ohms is a pretty common value so should not be impossible to find. Acro, Brooks, and Fairchild are ones I've used with great success. |
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| hacknet |
okay. thanks.
by that i assume that any ordinary iron would do rite? |
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| SY |
| Any iron? No. The quality of your circuit will be strongly limited by the transformer choice. It's the single most critical component. |
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| hacknet |
| no problem. i should be able to solve that problem;) |
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| fdegrove |
Hi,
| quote: | | Hi Frank, i've been wanting to make a PP 2A3 and been contemplating on the JE Labs PP 2A3. However, I want to try one of yours. Is that at all possible? Share the schematic or is this a commercial amp? |
ArnoldC,
It's not a commercial amp but I still have to draw a schematic.
I'll post it when it's done.
In the mean time, thamks for the confidence you put in me.;) |
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