PP3521 idht

[Paul Barker]

Iv’e found 3 mesh 27’s

[Paul Barker]

So Ive been calculating (sadly Ive lost the A “(A)ctual gain” spreadsheet I made to speedily come up with A which is less than mu)

So in RCL coupling that I plan for two stages of 27:

1/ the load is anode load resistor parallel with grid choke. The worst case scenario load would be the max permitted grid resistor 150,000 ohm. I know the grid choke is greater equivalent than that. Parallel with load resistor 47,000 = 36,000 ohm

2/ Im not bypassing the cathode resistor (360 ohm) so , quick digression to compund curves internal resistance is 11,000 ohms I think effect of unbypased cathode resistor is mu+1 x rk added to internal resistance mu from compound curves 8.5 (9.5*360= 3420+11000 = 14420) source resistance.

”A” becomes 6.07 per 27 stage squared for two identical stages = 36.84

Working backwards from pp3521 max power requires 25v peak 17.7 v rms / 36.84 = 0.48v rms, as this is more likely >/= 1vrms we have enough headroom and can go without cathode bypass caps.

I decided the idea of IT’s would require expense by the way, and involved compromise to keep the expense not too great. Any expense is too great in the end, the parts for rcl I have already.

There are two coupling caps. Im going to try paper in oil first.

I also have 4 nos 37’s, but have a fourth mesh 27 on order, so 37’s are only in reserve.

[ACPEN]

Hi - I too have tried the PP3521 in SE using drivers recommended to drive PX4's but was never happy with the results - these were the H42 and AC/S2PEN types.
Since seeing this thread I decided to try again using MH4's as drivers- good,
but slightly low gain, I then tried MH4's in mu follower configuration - the outcome being higher gain and lower output resistance - this did the job and well worth a try if you haven't settled on other means yet, but don't overlook elevating the heaters.
Rgds
David.

[Paul Barker]

Thanks for the input. Srpp totem pole mufollowers ccs’s pentode ccss’s I havent used for over 23 years, not my bag but if I fail I’ll know why. I’ll keep it simple first. If it needs lower impedance drive it can get another way of reducing that. Trying to stick to idht’s and would rather use 1920’s 1930’s idht’s. But i could easily cheat with 6em7 power section driving the output valve. I’ll not do that unless necesary.

So with sufficiently low impedance drive did you like the pp3521?

[ACPEN]

Yes, I like the PP3521 and have done for some time, also the PEN3520 which although a pentode makes a reasonable sub and can be a direct plug in.
I too have used the USA types, UY-227 and UY- 224 (tetrode) but came back to the British types of the same period, MH4 being also from the 30's. Be interesting to hear your thoughts should you stray into SRPP or Mu follower territory. I should say that I also tried the pentode mu follower version but decided against - I find the triode Mu follower 'sound' very similar to the common cathode RC configuration.
Good hunting!

[Paul Barker]

Thanks.

[ACPEN]

Just to say that have broken with tradition (my own) and have tried a 'modern' approach as a driver - an E810E ! in pentode mode - 10k load, 150v S.G, 100R bias. 200v ht, runs at approx 14mA - sounds Good, certainly worth a try if anyone is still looking for driver options for the PP3521 triode. To be honest after listening to 300b amp for some time, very little difference.
Caveat, my ears are 81 yrs old!
D.

[ACPEN]

Ooops!
E810F or E180F pin compatible if you leave pin 6 disconnected.