The Amp Garage

This may give you some hints to the Standel S80 circuit arrangement.
http://www.ozvalveamps.org/playmaster/pm117cct60w2.gif

The OD3 would be the 6DQ6 screen grid regulator.
The 6U8A would be arranged much like the 6BL8 in the posted circuit.

6DQ6 are great in Git Amps.

Cheers,
Ian

With a post phase inverter cut control the feedback will act to oppose that cut by increasing its output at the cut frequencies. You may well end up with problems in the phase inverter as it runs out of output voltage swing. Particularly with a cathodyne phase splitter. Not sure if it has ever been...

With a post phase inverter cut control the feedback will act to oppose that cut by increasing its output at the cut frequencies. You may well end up with problems in the phase inverter as it runs out of output voltage swing. Particularly with a cathodyne phase splitter. Not sure if it has ever been ...

Is it between 1962 and 1972?
If so look here:
http://www.standelamps.com/support/sche ... index.html
Cheers,
Ian

The PI needs the "best" CCS. I started with a single transistor CCS with a LED reference. So that configuration is better than others with more components? So I don't get why overcomplicating it with more components. As a "Rule of Thumb" the -ve supply should be at least X3 the bias voltage. Thanks...

Yes that is it. Current Source loaded Mosfet source followers plus the Baby Huey feedback scheme, balanced shunt feedback from output tube anodes Cheers Ian Thanks, so from your design I see that there's no need to double the bias voltage to get linearity, 1.5 times is enough with that design of CC...

roberto wrote: ↑Wed Nov 28, 2018 7:15 am Hi Ian,

is this one the design you are referring to?

Yes that is it.
Current Source loaded Mosfet source followers plus the Baby Huey feedback scheme, balanced shunt feedback from output tube anodes
Cheers
Ian

Yep
effective load at high frequencies is 200K The cap effectively bypasses the 100K. gain is reduced to 2/3.
effective load at low frequencies is 200K + 100K = 300K

The half gain change frequency (when Capacitive Impedance = 100K) is at 3183 Hz.

Cheers,
Ian

NOT POINTLESS EVER A tube cathode folower or mosfet source follower between phase splitter and output tube grid allows us to not repeat the bad design of most guitar amps, over many years. What is wrong with those designs - inadequate control of the output tube grid by use of too high a grid leak re...

I did an analysis of this.
For your possible interest see my (Gingertube) post here:
https://music-electronics-forum.com/sho ... 2#poststop

Cheers,
Ian

I built a "standard" from TUT5. Powerscaled. I chnaged the Power section slightly to run a quad of 6V6. Also modified the Fixed/Cathode bias switching to operate on a per pair basis Similarly changed the pentode/triode switching to a per pair basis. I mostly run it with one output pair in fixed bias...

JUst something to watch. I restored one of these and had intermittent volume drops after the restoration. Turned out to be the 0.01uF cap which feeds the preamp signal into the phase splitter of the power amp section. Mechanical failure of that cap. When I desoldered it, it came out in 2 pieces. It ...

The balance resistor thing is one of those buried tech things. Because the caps are in series and have the same charge and discharge currents through them, they will share voltage according to the cap values. 2 equal value caps will share the voltage equally. There are 2 things which can screw up th...

Power Scaling is achieved by a variable high voltage supply applied to the output tubes, anode connections via the output transformer centre tap and screen connections. For a cthode biased output stage that is all that is required. For a fixed bias amp you need a tracking bias supply regulator too s...

A couple of "off the cuff" commects. The gain of a cascode is approx. equal to the gm of the lower triode x the upper triode load resistor - so use the higher gm 12AU7 half of the 12DW7 as the lower triode. Just finished a Gibson GA40 Les Paul Clone - didn't have any 5879 pentodes so I used 6BR7 sin...