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Greetings all I'm new here and was hoping some of you fellas/gals would give recommendations for a stereo PP 6v6 amplifier I have two older Sansui outputs.I have a few power transformers too. I have built a few guitar amps but never tried a tube stereo amp. Any Icons that come to mind? Thanks!
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One of my favorite amps is a 6V6 in triode mode. 6CG7 voltage amp direct coupled to a 6cg7 split-load invertor. No feedback, B+ around 300 volts, 10K output transformers. Very simple and straight forward. Sounds very nice IMHO. Only "special" parts are grid chokes on the 6v6's...all motor run caps if you call them special....CLCRC power supply....old 5U4 RCA coke bottle rectifier. Parts count is low so affording decent resistors and such is no big deal.
Only downside is it is good for all of 2 watts class A1 going downhill. Seems I'd have to clip it now and then but sure can't hear it happening. Plays crazy loud with audax pro170mo (also did well with 12" alnico by RSC) and 18sound nd1090 (passive crossover at 2khz) from 125 hertz and up. Call the speakers about 99db/watt.
Well I thought I'd use these speaker I bought from the second hand store.
DENON SC-M51 not the most efficient speaker for this plan (I think 88db) but they were 16.00 for the pair :). I thought there might be something wrong with them. I got them home and they sound great through my old Adcom gfa-545 and Apt Holman preamp that I've had forever. Like I say I have built guitar amps but never Hifi.I was always kinda intimidated. When I look at the schematics many of them seem simple enough. Thanks for all the suggestions so far really appreciate the feedback/help.
https://www.youtube.com/watch?v=IGDsZh3mMqc
Tube watts are precious. To get more forces you into pentode, ultralinear, or tetrode mode. Doing that forces you into feedback. All of that forces you into a much greater understanding of electonics and the need for better measuring devices. If you can avoid all of that it is much simpler to build something that sounds good (IMHO).
Speaker efficency is the key to that goal. If you can put together something that presents a constant impedance at a reasonable XXdb/watt then you can forego feedback and high wattage. I have found that looking at pro audio speaker offerings is the ticket. I also think it pays to consider an active crossover and and bi-amping. Real bass takes serious wattage best served by a solid state amp.
Just my 2 cents based on what I have discovered over the years. Certainly you can build a higher wattage amp and use more traditional speakers but I find that a harder way to to go.
Russ stated a fundamental truth. Regardless of technology, proper mating of amps and speakers is crucial to obtaining a good result.
Paul Joppa has provided the 'phile community with a useful rule of thumb, for mating amps and speakers. Joppa's Rule states that in an "average" listening space an amp/speaker combo should be capable of producing 102 dB. SPL peaks at a 1 M. distance. Even if the Denon speakers are honestly rated and "tube amp friendly", they are not suitable for use with any amp you can make using the "iron" already in your possession. To make matters worse, many commercial speakers need to be rerated, when combined with tubed power amplification. A nominal 8 Ω speaker that exhibits substantial dips in its impedance curve, especially in the bass region, has to be treated as being 4 Ω, when mated to a tube amp. Another "gotcha" is a speaker that is 4 Ω and rated at nn dB. for 2.83 V. of drive needs derating by 3 dB., as 2.83 V. into 4 Ω is 2 W. Tube power amps, with their O/P trafos, produce the same power on all the speaker taps.
Eli D.
Thank you for that very informative reply. This is going to take some thought and planning and I'm up for it :)
Most of them are wide range and efficent. Could make the start of a good set of speakers. We all know a 6v6 guitar amp can play pretty loud.
Yeah what you say makes sense. What started this was my signal tracing of a el84 guitar amp while I lay on my bed. I fixed the problem then laid there listening to my ipod through the guitar amp and a single Reverend Alltone 12 inch speaker.Maybe it was the glow between my ears and satisfaction of getting that amp going, but i really enjoyed the music while i drifted off for a "little nap"
Edits: 01/22/15
A fellow once made a remark to the effect that a tubed HIFI amp is a guitar amp gussied up in lipstick and nylons. It's a bit more complicated than that, but many circuit elements are common to both applications.
While a guitar amp is a distortion machine controlled by the player, a HIFI amp is supposed to reproduce that which the performer(s) laid down.
Eli D.
Power is why we made "El Cheapo" AB1, but close to Class "A". Most of the time, both triodes are conducting. Only when peak power is produced, do the "finals" alternately cut off. Poinz's "Musical Machine" employs a similar operating conditions set. Both designs yield approx. 6 WPC from the triode wired pair.
Eli D.
Sansui audio transformers pulled from what model?
Actually its ive had them so long they could be HK too honestly cant remember but I know it was a 6v6 amp.
A picture, including a ruler, will help. If the "iron" came out of something like a H/K FA3000 receiver, build a triode mode "El Cheapo". That stuff is undersized for the claimed 15 WPC.
I strongly suspect your transformers did not come from a Sansui product. The 500A used 6BM8 "finals", while the 1000A used 7591s.
Eli D.
The iron in my 500A is huge...not so much for 500.
The Mind has No Firewall~ U.S. Army War College.
Thanks for the info, I have some bigger transformer too ill post the info latter
I'm not home right now.
I'm not sure the transformers are stamped ft34239963 8316101
"the transformers are stamped ft34239963 8316101"
I'm pretty sure that's an HK number. Can you post a photo next to a pencil or something like that for scale? How much power do you need from this amp? There's a big difference between triode mode and pentode.
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Buy Chinese. Bury freedom.
I'm almost 100% sure these are the OPT's in the link below. The scale shape etc seems correct.there are what appears to be 8 and 16 ohm taps (green and yellow.)
http://shermanr.web.prw.net/A300_TOP.jpg
Those trafos look like the undersized stuff in a FA3000. Notice the relationship between the model #s. They should be FINE in a triode wired "El Cheapo". I suspect the "iron" is good enough to permit the use of of a 0.068 μF. cap. and a 120 Kohm resistor in the I/P high pass filter, instead of the 0.056 μF. and 100 Kohm parts shown in the schematic.
The "6" WPC a triode wired "El Cheapo" yields combined with speakers of 94 dB. sensitivity will be adequate for all but the most demanding material. The digital cannons in Telarc's 1812 Overture recording might be overdoing things. ;> )
Eli D.
Sorry for the poor pic its taken with my ipod and thats a dime for reference :) I think these came out of a an HK a300 pretty sure. I want nice mids etc I have a small sub I can use to get the jod done for bass but yeah not going for high volume just low to moderate.
one more pic
Here is a side view
Eli's correct about these being smallish for 6V6s. Still, they'll definitely output more power within their limits in pentode mode than triode. I'm pretty sure those transformers were used in both the A-300 amp and TA-224 receiver. You should be able to make a good performing amplifier with them.
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Buy Chinese. Bury freedom.
This design has gotten good peer review on DIY forums.
Poindexter's "Musical Machine" is excellent, but it is quite costly to build.The "El Cheapo" project I'm associated with is topologically related, but is considerably less expensive to execute. Remember the 'AQ5 is, for all practical purposes, a 6V6 in a 7 pin mini package.
These triode wired designs yield approx. 6 WPC and mid 90s or higher sensitivity speakers are indicated. "El Cheapo" can be used with pentode mode "finals", for more power O/P. However, practical feedback from the field about that option is not available. The Hashimoto "iron" Sansui used is well respected.
Eli D.
Edits: 01/21/15
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