Hello everyone, I'm looking for a simple push pull circuit to use with the Dynaco A470 OPT. The pri. Z is 4.3k and it has screen taps. I have a hefty 400v B+ power supply, and would prefer to use all octal tubes. I'd like to find something very basic and uncomplicated. Any ideas would be greatly appreciated. Thanks, Jay
What are you planing on driving?
http://www.audiotropic.net/Projects/ampEL34.html
There is a newer version of this circuit that has a 6GK5 LTP driving the EL34's. I would be more than happy to post it but I would like Poinz's permission first. I know he is very kind to the DIY community being a DIYer himself, I just don't know how liberal he has been with this design.
http://www.audiofanatic.it/Schemi/Tipo/Valvole/finali/pic_finali_PP/EL34PP_6CG7_EF86_Dyna_Mull.jpg
I know, a different output transformer, but just a thought. I had an idea to try this circuit in the future but with a 6J7 input and 6SN7 splitter/driver. Hard to get simpler than Poinz's EL34 amp (linked), add uses octals as requested. 400v B+ is a tad high but with a tube rectifier or choke input that can be tamed.
Good luck and happy listening!
Cheers
James
http://www.audiotropic.net/Projects/ampEL34.html
There is a newer version of this circuit that has a 6GK5 LTP driving the EL34's. I would be more than happy to post it but I would like Poinz's permission first. I know he is very kind to the DIY community being a DIYer himself, I just don't know how liberal he has been with this design.
http://www.audiofanatic.it/Schemi/Tipo/Valvole/finali/pic_finali_PP/EL34PP_6CG7_EF86_Dyna_Mull.jpg
I know, a different output transformer, but just a thought. I had an idea to try this circuit in the future but with a 6J7 input and 6SN7 splitter/driver. Hard to get simpler than Poinz's EL34 amp (linked), add uses octals as requested. 400v B+ is a tad high but with a tube rectifier or choke input that can be tamed.
Good luck and happy listening!
Cheers
James
Hi jay,
Your voltage is well within the range of 6L6GC designs. With a higher plate dissipation rating than EL34 types, these might be what you are looking for. It would be nice to stay with normally accepted tubes (nothing odd) to make things simpler. Your primary impedance will work with both 6L6GC types and also 6CA7 / EL-34 types. I find the 6CA7 "fat bottle"is more robust than the EL34 thin bottles. You could even use 6550A / KT-88 types, just don't push the outputs too hard, the core might saturate. This is more of an issue at higher powers with lower frequency response.
The simplicity of a design will not change much between tube types. A fixed bias would allow higher power, but that comes at a price. You'll have to set the bias currents periodically.
Understand too, a small increase in complexity can really pay dividends when it comes to sound quality - or not. Depends on what you do. You have decent iron, so make a good circuit worthy of that iron.
Do you have any idea how much power you'd like? What speakers are you planning to drive, and to what levels? How large is your room? Do you expect any major changes in your living quarters or sound equipment? If so, aim for your new circumstances. If you have to trade power for low end response, go for the lower frequency response.
One thing for sure. Make your chassis large enough so that you can space your tubes out, and transformers. Too small a chassis will bring trouble with heat and probably supply noise as well. A stereo chassis is reasonable for this power class.
-Chris
Your voltage is well within the range of 6L6GC designs. With a higher plate dissipation rating than EL34 types, these might be what you are looking for. It would be nice to stay with normally accepted tubes (nothing odd) to make things simpler. Your primary impedance will work with both 6L6GC types and also 6CA7 / EL-34 types. I find the 6CA7 "fat bottle"is more robust than the EL34 thin bottles. You could even use 6550A / KT-88 types, just don't push the outputs too hard, the core might saturate. This is more of an issue at higher powers with lower frequency response.
The simplicity of a design will not change much between tube types. A fixed bias would allow higher power, but that comes at a price. You'll have to set the bias currents periodically.
Understand too, a small increase in complexity can really pay dividends when it comes to sound quality - or not. Depends on what you do. You have decent iron, so make a good circuit worthy of that iron.
Do you have any idea how much power you'd like? What speakers are you planning to drive, and to what levels? How large is your room? Do you expect any major changes in your living quarters or sound equipment? If so, aim for your new circumstances. If you have to trade power for low end response, go for the lower frequency response.
One thing for sure. Make your chassis large enough so that you can space your tubes out, and transformers. Too small a chassis will bring trouble with heat and probably supply noise as well. A stereo chassis is reasonable for this power class.
-Chris
Jay,
Your O/P "iron" was intended for use with EL34s. As 6.6 K trafos are "routine" with 6L6s, I'd stay with the EL34/6CA7/KT77 group. A 400 V. B+ rail is not particularly "tall". Use "fixed" bias on the O/P tubes.
Simple and all Octal you say. How about a Mullard style circuit with a 6SJ7/5693 as the voltage gain tube and a 6SN7/5692 as the LTP? CCS load the splitter tail with a 10M45S, instead of a resistor. If push comes to shove, you can always buffer the splitter with IRFBC20 MOSFET source followers.
Your O/P "iron" was intended for use with EL34s. As 6.6 K trafos are "routine" with 6L6s, I'd stay with the EL34/6CA7/KT77 group. A 400 V. B+ rail is not particularly "tall". Use "fixed" bias on the O/P tubes.
Simple and all Octal you say. How about a Mullard style circuit with a 6SJ7/5693 as the voltage gain tube and a 6SN7/5692 as the LTP? CCS load the splitter tail with a 10M45S, instead of a resistor. If push comes to shove, you can always buffer the splitter with IRFBC20 MOSFET source followers.
Interesting ideas guys, thanks. I'm still struggling to learn this stuff, so some of that went over my head. I've built several amps, but pretty much have to follow a schematic, for the most part. I was looking at an early Sherwood design (the S1000), which is certainly simple enough, but the OPT Pri. Z is 5500, compared to the Dynaco's 4300 (it's a 6L6 design). I certainly wouldn't object to a more complicated circuit, but it would have to be in the form of a schematic. I hate coming right out and asking for schematics, but untill I get a better grasp of things, I'm sort of stuck.
You could consider the Williamson with EL34's too. I would try a few things things though when you settle on a design. First would be to wire the EL's at triodes, unless you need more than 14-16 watts. The second would be to try it free of NFB, then if you need feedback slowly add it little by little.
OK I did some searching and I found the other schematic I was talking about posted around here so I will go ahead and slap it up. ...Poinz, if you read this and don't want it up I will have a mod take it down...
It doesn't use all octals like you requested but it is a simple and elegant way to get about 16watts from the minimum amount of gain stages. I talked with Poinz through email about this one, I have since deleted that email, but what I got was he liked this one better than his first EL34 amplifier (the one I linked).
OK I did some searching and I found the other schematic I was talking about posted around here so I will go ahead and slap it up. ...Poinz, if you read this and don't want it up I will have a mod take it down...
It doesn't use all octals like you requested but it is a simple and elegant way to get about 16watts from the minimum amount of gain stages. I talked with Poinz through email about this one, I have since deleted that email, but what I got was he liked this one better than his first EL34 amplifier (the one I linked).
Attachments
Hi Eli,
-Chris
True, classic for 6L6 types. However, you can also use 4.3K for 6L6 types also. This is probably more common at higher powers and a quad of 6L6s. I wonder what a quad of 6BQ5s would sound like with this transformer.
-Chris
hey-Hey!!!,
I'd recomend the E-Linear 6L6GC. 6AC7 pentode front end LTP/diff amp will keep you all-Octal. Micah heard this one built into my Heathkit W6m amps and can give you an opinion if you ask. It is simple, two stage and does not require loop NFB. It can take SE or balanced input( I do mine balanced in the Heath, and SE on the Dyna Mk.iii ).
cheers,
Douglas
I'd recomend the E-Linear 6L6GC. 6AC7 pentode front end LTP/diff amp will keep you all-Octal. Micah heard this one built into my Heathkit W6m amps and can give you an opinion if you ask. It is simple, two stage and does not require loop NFB. It can take SE or balanced input( I do mine balanced in the Heath, and SE on the Dyna Mk.iii ).
cheers,
Douglas
I am presently breadboarding Poindexter's 6GK5 amp shown above, and I was considering using a 5AR4 rectifier since my power transformer voltage was higher than 310V or so, but I only had the SS rectification PS schematic provided by Poinz.
Thank you for the 5AR4 PS schematic!
I'm sure I'll also have lots of newbie questions once the build is close to being finished. I'm using Hashimoto HW-60-5 output transformers and a one electron Power transformer.
Thank you for the 5AR4 PS schematic!
I'm sure I'll also have lots of newbie questions once the build is close to being finished. I'm using Hashimoto HW-60-5 output transformers and a one electron Power transformer.
The EL34 from Poinz is on my list of projects and I for one would be very interested to hear your results! Especially with Hashimoto iron, for some reason their little cubes of iron really draw my attention. I was thinking of using Magnequest iron though in my version. Right now though I am slowly part shopping for Poinz's 6V6 Musical Machine. I have reevaluated my needs and the glorious 5watts or so should do it for me; but I can say for sure, one of the EL34 Machines will grace my household eventually. I think I am going to get Jack at Electra-Print to wind me some cute little outputs for the 6V6 Machine.
...sorry, slowly headed OT
Oh, and no problem with the 5AR4 schematic, Poinz was nice enough to send me both via email. Great guy and I am sure he would be willing to help with your build, along with all of us here!
Cheers
James
...sorry, slowly headed OT
Oh, and no problem with the 5AR4 schematic, Poinz was nice enough to send me both via email. Great guy and I am sure he would be willing to help with your build, along with all of us here!
Cheers
James
David Hafler designed the Dynaco O/P trafos to be used inside a global NFB loop. I'd like better "iron" for Doug's Elinear circuitry.
Gain is certainly adequate with Williamson topology, but there are significant stability issues, unless O/P trafos of the highest quality are employed. OTOH, Mullard topology is much less likely to have stability issues.
Mullard style circuitry employs a common cathode voltage amplifier DC coupled to a LTP (differential) phase splitter, and (naturally) PP "finals". The schematic for the "classic" Mullard 5-20 amp is here. The is no need to repeat Mullard's choices for a tube complement or O/P stage biasing. BTW, the original 5-20 has WAY too much gain, when a CDP is the signal source.
Gain is certainly adequate with Williamson topology, but there are significant stability issues, unless O/P trafos of the highest quality are employed. OTOH, Mullard topology is much less likely to have stability issues.
Mullard style circuitry employs a common cathode voltage amplifier DC coupled to a LTP (differential) phase splitter, and (naturally) PP "finals". The schematic for the "classic" Mullard 5-20 amp is here. The is no need to repeat Mullard's choices for a tube complement or O/P stage biasing. BTW, the original 5-20 has WAY too much gain, when a CDP is the signal source.
Eli Duttman said:
I like the look of that circuit, and it's certainly "no frills". I will look at it and see if I can figure out how to swap octals into the front end.
Hi Eli,
The iron you have should be used with a stable, forgiving design. Just so layout is not as critical. I don't care much for the original schematic using the 7199. Never mind the expense of this tube.
-Chris
Yup.
Certainly!
The iron you have should be used with a stable, forgiving design. Just so layout is not as critical. I don't care much for the original schematic using the 7199. Never mind the expense of this tube.
-Chris
hey-Hey!!!,
I'd also suggest Eli's El-Cheapo design. It is two stage, LTP feeding the finals. There has been many built and there's no issue scaling it. The input/phase splitter is a twin triode and there's lots of options there especially if you've got a linestage with gain. Its short loop of NFB is easy to adjust and poses minimum risk for oscillation.
Build it with fixed bias, run class A, and with a good MOSFET ccs for the input stage cathode load and you're off to the races.
cheers,
Douglas
ps. the note from Eli suggesting the A470 is designed for use insice a FB loop points towards its quality IMO. The E-Linear design uses even shorter FB path and should be more tolerant of OPT parasitics and accompanying phase shifting issues.
I'd also suggest Eli's El-Cheapo design. It is two stage, LTP feeding the finals. There has been many built and there's no issue scaling it. The input/phase splitter is a twin triode and there's lots of options there especially if you've got a linestage with gain. Its short loop of NFB is easy to adjust and poses minimum risk for oscillation.
Build it with fixed bias, run class A, and with a good MOSFET ccs for the input stage cathode load and you're off to the races.
cheers,
Douglas
ps. the note from Eli suggesting the A470 is designed for use insice a FB loop points towards its quality IMO. The E-Linear design uses even shorter FB path and should be more tolerant of OPT parasitics and accompanying phase shifting issues.
This El Cheapo?
http://homepage.mac.com/planet10/forum/elCheapo-23jun06-map.gif
As far as I know the transformers wouldn't be suitable for that design(?). See the EL34 I posted above with the 6GK7 input, it is more or less the same design but with outputs that would play nicer with those transformers. Correct me if I am wrong.
Cheers
James
http://homepage.mac.com/planet10/forum/elCheapo-23jun06-map.gif
As far as I know the transformers wouldn't be suitable for that design(?). See the EL34 I posted above with the 6GK7 input, it is more or less the same design but with outputs that would play nicer with those transformers. Correct me if I am wrong.
Cheers
James
jaymanaa said:
The CJ MV75 is relatively simple and better sounding than most "rivals"
of its time. A classic design, I would say.
I would just improve the bias supply using a bridge and a good CRC filter.
http://www.bonavolta.ch/hobby/en/audio/mv75.htm
If you like to use all octal tubes you can replace, without any other change in the circuit, the 5751 with the 6SL7 and the 6CG7 with the 6SN7.
In place of the 6550 I would go for the JJ 6L6GC.
Cheers,
45
P.S.
I just forgot an important detail. Almost certainly you will have to adjust the feedback network, in the first place because you are using a different OPT and then also different tubes.
I just forgot an important detail. Almost certainly you will have to adjust the feedback network, in the first place because you are using a different OPT and then also different tubes.
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