Yes the cathodyne is always balanced, provided it is symmetrically loaded. In that circuit you can see that as far as AC is concerned, the cathode is loaded by R2||R5 which together make 20k, which matches the anode resistor R4. (R1 and V1 are very high impedance so they have negligible impact on balance in this example).
http://www.r-type.org/articles/art296d.jpg
Got some numbers and/or measurements for this?
Peter & Merlin, do you think the almost universal move to the LTP in the last of the great valve/tube amps was a marketing scam? This is a serious question. I worked with one or two of these designers .. sadly no longer with us so I can't check on their reasons.
The real stopper was the very low NFB, which were fixable. But then the other shortcomings
was even more clear.
Just to mention the disciússions on "which 12AU7 variant that sounds better" exposes that something is
missing. You never have any discussions over which 7199 ( or similar) sounds better or worse in a
genuine ST-70.
My recollection is that half a percent dist was present even at low power and driving one channel
it was not even up to 35w before dist rises steeply.
There is a youtube channel that confirms my observations.
As for what phase inverter to use , all of the known could sound ok. Mr Erik "Ttiode" Andersson favored paraphase
inverters, so did johnson in AR Dual 75, leo fender used LTP and Dynaco designs used confortina. Transformer
is not used as far as i know.
Of them confortina and transformer is the only that needs no adjustment and is inherently symmetric when used
within it's limits.
LTP and paraphase is dependent on some measurment to adjust, and are sensitive to tube differences.
( This is my personal view as layman )
was even more clear.
Just to mention the disciússions on "which 12AU7 variant that sounds better" exposes that something is
missing. You never have any discussions over which 7199 ( or similar) sounds better or worse in a
genuine ST-70.
My recollection is that half a percent dist was present even at low power and driving one channel
it was not even up to 35w before dist rises steeply.
There is a youtube channel that confirms my observations.
As for what phase inverter to use , all of the known could sound ok. Mr Erik "Ttiode" Andersson favored paraphase
inverters, so did johnson in AR Dual 75, leo fender used LTP and Dynaco designs used confortina. Transformer
is not used as far as i know.
Of them confortina and transformer is the only that needs no adjustment and is inherently symmetric when used
within it's limits.
LTP and paraphase is dependent on some measurment to adjust, and are sensitive to tube differences.
( This is my personal view as layman )
Was it almost universal though? I haven't done a survey! Certainly it would not have been a scam. Amplifiers got more powerful, so more would be using bigger bottles that need more drive voltage, which a cathodyne might struggle with. And the cathodyne has always foxed a lot of designers -Byrith is a perfect example- whereas the LTP was well established early on. So I guess it may have become just another 'design trend' to use an LTP.
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A LTP with a high impedance CCS as it's tail and with equal plate impedances doesn't need any adjustments, nor is it sensitive to tube differences. Can't state for the Paraphayse, though.
Best regards!
"A LTP with a high impedance CCS as it's tail and with equal plate impedances doesn't need any adjustments, nor is it sensitive to tube differences."
True as long as the triode halfs are similar. But it's also a more complicated setup
True as long as the triode halfs are similar. But it's also a more complicated setup
I'd say that in a wide range of applications both LTP and Concertina are fine. My usual approach is:
- anything that requires <= 20Vp for the output tubes, I use Concertina
- For the rest, LTP.
Many many years ago it has been shown here that even with rather dissimilar triodes, such as half a 12AU7 and half a 6922, AC symmetry is granted. It is really easy to comprehend: If the plate current in one triode rises by some amount, the plate current in the other triode consequently falls by exactly the same amount, and vice versa.
Best regards!