3C24SE amp...

[Guiness]

Was checking out Valve World last night and came across this amp...

Just curious as to what you guys think of this circuit.

Thanks

[Fuling]

Looks like a version of Shishidos "Dynamic Coupling". Should work fine, but personally I would choose a driver tube with lower rp and higher gm.

[316a]

Originally posted by Guiness
Was checking out Valve World last night and came across this amp...

Just curious as to what you guys think of this circuit.

Thanks

Built a similar amp last year . Used 3A/108A input stage and 6AH4 driver . LCL DC filaments all round (only ac for the 6AH4) , feedback implemeted anode-to-anode between input and output valve , also the output transformer secondary was in the cathode circuit of the 3C24 . It sounded pretty good but never made it past breadboard stage , the 3C24 is an impressive looking valve running full cherry One point to note is that A2 amps sound very bright and can sound unusual on bass reflex speakers . If attempting a similar amp , the grid and plate dissipaters need to be used

cheers

316a

[316a]

schematic

[Guiness]

I ran across 6 of these tubes the other day while I was re-arranging some boxes and thought they would make a pretty good amp. I will start gathering up some parts and try acouple different circuits.

Will post some pictures soon.

Thanks guys

[316a]

Originally posted by Guiness
I ran across 6 of these tubes the other day while I was re-arranging some boxes and thought they would make a pretty good amp. I will start gathering up some parts and try acouple different circuits.

Will post some pictures soon.

Thanks guys

Don't forget the heat dissipators ! These won't last long otherwise . Also run the filaments for a few hours to clear any residual gas as these are self-gettered (anode is coated with the getter material)

cheers

316a

[coresta]

Hello 316a , how do these DHT die ? or when are they dead ? filament failure or something else ? i have some HK54 and VT127a left . They're not new , they light on but i dunno about the vacuum . Should a sherry red heating of the plate clean them new ? cheers Pierre

[316a]

Originally posted by coresta
Hello 316a , how do these DHT die ? or when are they dead ? filament failure or something else ? i have some HK54 and VT127a left . They're not new , they light on but i dunno about the vacuum . Should a sherry red heating of the plate clean them new ? cheers Pierre

The weak points of all those valves are the seals . If the seals get too hot then air gets in and it's game over for the valve . I have over a dozen VT127A and there are a few really gassy ones so these could probably do with a good baking either in the oven or by lighting the filament . Incidentally it's a nasty one to light up and will need DC , you will need some huge chokes for the filament supply , regulators , resistors etc just drop too many volts . HK54 are a handsome valve , I've some of these but never used one , the same will apply , bring them up slowly on a variac and run the fils for a few hours . Better still run your HK54 and VT127 from an external filament supply and run on a valve tester using the filament as the cathode connection . From memory the VT127 should have gm of around 1.8mA/V at 0V / 400V . See picture for a messy breadboard using VT127 , the chokes at the back are the LCL filament supply

cheers

316a

[coresta]

Originally posted by 316a


The weak points of all those valves are the seals . If the seals get too hot then air gets in and it's game over for the valve .

for sure , they go hot hot hot , even after 5 minutes . I have done black clips from ... transistors coolers Do you think these are worth the effort ? Not with AC heating ? huh ? ! best regards
Pierre

[316a]

Originally posted by coresta

for sure , they go hot hot hot , even after 5 minutes . I have done black clips from ... transistors coolers Do you think these are worth the effort ? Not with AC heating ? huh ? ! best regards
Pierre

You can try with AC heating , I could not completely remove the hum though . VT127 will be more robust than the 3C24 without dissipators . Get yourself some HR6 caps for the 3C24 which are only $5 per piece (Google it , think it was Nebraska Surplus who had some) . My father turned me some caps for the VT127 , I'm sure you could drill out an HR6 to suit otherwise

cheers

316a