• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Dynaco Stereo 70 amplifier

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#61
I'll comment....

I purchased a VTA driver board and really liked the improvement over the stock board. The 12AT7's sound more detailed and clean.
The ability to adjust each tubes bias was nice.


With respect to cathode resistor value... tried it and couldn't hear a difference. I guess you can believe what ever suits you.
 
#68
Well, looks like it will get "Curcio--itated" along the lines of the 1989 Glass Audio article -- except I will use the LR8N3 regs and triode the output.

I simulated the output stage with the best SPICE model of the 6DJ8 that I could find -- looks like you could use it as a VLF transmitter on the newly opened up slice of the band made available to US ham radio operators:

An externally hosted image should be here but it was not working when we last tested it.
 
#71
Banderwhatever -

Would you could to share the wisdom behind those suggestions?

I've been happily listening to that circuit for 17 years, with both EL-34's and 6B4G's. But maybe my acoustic guitar and banjo picking ears don't know what actual music sounds like.
 
#73
CharleyW said:
Banderwhatever -

Would you could to share the wisdom behind those suggestions?

I've been happily listening to that circuit for 17 years, with both EL-34's and 6B4G's. But maybe my acoustic guitar and banjo picking ears don't know what actual music sounds like.
Click to expand...

hey-Hey!!!,
The short answer is that it will work better.

There is signal at the cathode node, yet the upper grids( effectively the screen grid in this pentode construction ) is ref'd to ground. I offered one wat to ref. them to the cathodes. There are other simpler ways to do it.

Second eliminates the front-to-back loop NFB. Using the U-L taps this way( termed E-Linear http://www.pmillett.com/ scroll down a bit ) offers short path plate to grid around the output stage. Shorter is better for FB path length IME.

As to your ears, I can't comment on their preferences, but after bulding about a half dozen amps with variations on this basic theme I have not found better sonics with loop NFB.
cheers,
Douglas
 
#74
jackinnj - if you mean the first review of the Curcio, Vacuum Tube Audio, GSI, the Van Alstine, and the one that used FET's whose name I can't remember, that review was conducted by Roy Mottram, who, co-incidentally WAS Vacuum Tube Audio. He liked his the most and Curcio's second, but given his predijuices (sp?), let's throw his out.

Dave Davenport then re-did it - and used the power supply regulator that Mottram did not. He thought that Curcio's was the best, IIRC.

Banderwhosits - I was just curious about your comments, un-substantiated as they were. Then again, I am running 6B4G's in this amp with zero feedback.
 
#75
CharleyW said:
jackinnj - if you mean the first review of the Curcio, Vacuum Tube Audio, GSI, the Van Alstine, and the one that used FET's whose name I can't remember, that review was conducted by Roy Mottram, who, co-incidentally WAS Vacuum Tube Audio. He liked his the most and Curcio's second, but given his predijuices (sp?), let's throw his out.

Dave Davenport then re-did it - and used the power supply regulator that Mottram did not. He thought that Curcio's was the best, IIRC.

Banderwhosits - I was just curious about your comments, un-substantiated as they were. Then again, I am running 6B4G's in this amp with zero feedback.
Click to expand...

What sort of substantiation would meet your approval? Did you read Pete's audioXpress article? Do you recognize how the Curcio circuit applies signal to the k-g2 voltage? It is simple enough for you to substantiate for yourself I think.

Also, instead of butchering my moniker, just try "Douglas"
cheers,
Douglas
 
#77
CharleyW,
Doug has a pretty specific, and recognizable posting style, and he's been here a very long time so we're used to his quite cheerful and forceful mode of expression.

Doug is one of the most saavy and helpful people posting on these boards, and his advice has always been very high quality.

You might want to reconsider looking beyond the presentation and at the message itself, there might just be something useful there.

He's one of the good guys here, and I think your very derogatory responses to his comments were quite unwarranted. You may not agree, but his post certainly wasn't intended to be disrespectful as your post most certainly was.
 
#78
hey-Hey!!!,
One single correction if you'd be so kind Kevin. Your comment should perhaps read, "as your posts most certainly were".

It is no big deal, there was clearly no interest beyond being nasty. He already owns a perfect amp. No further alteration could possibly improve it for him.
cheers,
Douglas
 
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