Home Speaker Asylum

General speaker questions for audio and home theater.

RE: Nice layout

Yes but so does Dennis' amp.

A 7b4 with a 280k ohm plate resistor has an output impedance of somewhere near 50k ohms.

Dennis says the HF starts to roll off at 15kHz using modern output tubes which have less interelectrode capacitance than old tubes.

Dennis said with a Sylvania 2a3 the roll off starts are 9kHz and with a RCA 2a3 the roll off starts at 11kHz.

That is pretty much in line with the math.

A 50k ohm drive impedance won't drive much output tube Miller capacitance.

The other issue is the current delivery capability (or lack there of) of a 7b4 running less than 1ma.

That Miller capacitance will need to be driven and that takes current. Current that the 7b4 is not able to deliver.

The other problem with the design (my friends and/or Dennis') is the power supply.

The low value caps and low value chokes with low DCR makes for a very unstable power supply.

It's not stable with the amp at idle. When you stat playing music through it all hell breaks loose.

But if some people like the sound of that sort of thing...... who am I to complain?

It's just that for an amp that costs 18k per pair, with "best amp ever made" verbiage surrounding it........I would expect more.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"



Edits: 03/13/17

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  • RE: Nice layout - Tre' 15:09:38 03/13/17 (0)

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