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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Unexpectedly good EL84 amp

@Bas, what a beauty.
Thank you!
Gorgeous!
Thanks!
By chance has any been able to compare the original TCJ version to the RH84?
I'm on record for saying the RH84 is a keeper! The devil is all in the details for me. If you have very efficient loudspeakers.... the RH84 to my ears sounds awesome! SE vs PP....it al depends on the speaker IMO. The TCJ sounds way better on my kids's speakers: Mission 753 (90dB). I tested the TCJ on those speakers...and they kicked ***. On my Bastanis open baffle...there is a lot less difference. Except for the typical pp/se things.
 
The more I look at this the more I like the idea of using it for the luggable. Idling at less than 33mA per channel it should run fairly cool. That is less current than SE.. I was a little concerned about the highish B+ but that was before I realized how cool the bias was.

If I build this (original TCJ circuit) with B+ about 20V lower that wouldn't make a significant difference in performance would it?
 
Very much tempted to try this with cross coupled bias. Given the use of 6N1P it seems appropriate ro use Soviet military bottles for the output tubes also. :)

Something like this. Don't worry about the 32ohm OPT that is from another project (I actually do have some 32 ohm drivers). The application I have in mind will likely have another low gain input stage and preamp out buffer. This amp will have a HP filter at the input as the preamp out will be going to a built in low frequncy amp (bi-amp setup).

BTW, Shouldn't there be a protection diode from grid to cathode on that Cathodyne?
 

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Garter bias works great, try it :)

Probably should have the diode, but I usually leave it out on setups like this that have a DC divider. On floating/self bias I use the diode.

Also- try the above with 15k rather than 30k for the concertina load resistors, it'll run a bit hotter but "flatter" with the added benefit of more equal current draw in the upfront triodes. Not a big deal but if not built yet, why not?
 
Also- try the above with 15k rather than 30k for the concertina load resistors, it'll run a bit hotter but "flatter" with the added benefit of more equal current draw in the upfront triodes. Not a big deal but if not built yet, why not?

Makes me wonder why he chose that operating point. It seems he usually tries ro keep the same idle current on successive stages to keep even PS loading.
 
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Actually, John Broskie gave a pretty thorough explanation for choosing these resistor values - similar to his reasoning in the Aikido. As I understand him, it has to do with maximum ripple/noise rejection, resp. cancellation. Also, he says that his values insure constant B+ current loading under music signal (if I understood it correctly).

Please read a bit further down on his blog entry; the explanation is buried a bit. He talks about it when he discusses the EL34 variant:
PS-4 & PS-5 Tube Power Supplies

Scroll down a bit and start reading at the paragraph that starts with "Now we move to the beginning, ..."

That paragraph and at least the next two paragraphs; in his description of the driver stage he also talks about noise cancellation ... ;)


Best regards, Claas :)
 
Reading through the blog post on the EL34 version he discusses and interesting local'ish FB scheme that is quite interesting in which the OPT secondary is floated and each end of the secondary fed back to their respective driver cathodes. The main downside that I see is that a failure of interwinding insulation puts B+ on the floating secondary but otherwise it seems to have some real merit.

I suppose I ought to start a new thread to discuss it though since it really doesn't apply to this particular amp.
 
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Lingwendil,

what would be the reason for running the Concertina hotter than John Broskie had set it ?

Would the main benefit be the evenly distributed DC current through both halves of the 6N1P ? And would the benefit of that again be the more even wear on the two halves of the tube ? Or does it have something to do with the drive capability of the Concertina ?

If it's just for more even tube wear, my approach would be to set up the tubes for the respective channels in mirror-like fashion - in one channel, the Concertina would be on the left half of the tube; in the other channel, it would be on the right half. That way, I could swap the tubes between sides from time to time and even out the wear.

When I look at the data sheet of both the 6N1P and 6N1P-EV, for example the inter-electrode capacitances, the two halves look pretty symmetric to me - anything that would speak against this approach ?

I am slowly gathering parts for building this amp ... just got 100 pieces of 30k 2W 1% metal film resistors, so it would be no problem to try out 30k as well as 15k (by paralleling two 30k) on the Concertina ...

Also, I plan to buffer the B+ for each 6N1P with a 35 uF MKP cap per channel, so I am not terribly afraid of "non-constant" AC current draw ... :)

Best regards,
Claas