cayin a-55t want to use el34

[blue andry]

Hi ,

i recently planning to use el34 tube in my 6550 cayin a-55t .

i ask the store owner whether i have to do some mod in bias resistor in my amp , he say's it not necessary , just do manual bias to dc voltage around 0.35v so i bought el34 eh matched quad from him.

i also read some does mod on bias resistor from 220k to 100k when they going from el34 into kt88 , but i thought el34 would ok with 100k bias resistor typically found on kt88 circuit .


When i pop in new el34 into my socket and want to do manual bias on bias pot my voltmeter read no voltage

Wait for the new tube to cooled off , pop out el34 and pop in my old 6550 .
read the bias pot with my voltmeter , got bias voltage read

any idea why my voltmeter read no voltage ?
will i broke my el34 because i don't do any mod to my amp ?
what kind of mod i should do to use el34 in my amp ?


Any help would be appreciated .
Thank u

[Palustris]

Without a schematic one can only guess what is going on. I think the problem is that the 6550 and EL34 have different connections on the socket. Pin one of the 6550 is a no connect; on the EL34 it is the suppressor grid. You may have to rewire the socket as well as change a bias resistor. Without a schematic I would leave well enough alone.

[jerluwoo]

you will need to make a connection from pin 1 to pin 8.

[blue andry]

Hi ,

I have checked the tube socket ,
pin 1 already jumpered to pin 8 ,
and i read that pin 3 socket connected to 46k resistor ,
pin 6 connected to 1k resistor and the other's side of resistor leg connected to
pin 4 of tube socket .

any idea ?

[blue andry]

hi ,
i relook the amp schematic ,
pin 5 was connected in series to 1k resistor (r1) and shunted to 120k (r2) resistor .
pin 3 connected in series to transformer and shunted with 46k (r3) resistor to pin 4 .
pin 4 connected in series to 1k resistor (r4) and series to transformer and got shunted by the same resistor shunted by pin 3 (r3).
pin 8 connected to 10 ohm resistor going to the bias pot (r5).

pin 8 already jumpred to pin 1 .

there is 22k resistor (r5) near the bias pot but can't figure the connection

r1 , r2 , r5 located near the bias trim pot .

please help ,

Thanks

[Palustris]

"i relook the amp schematic "

Let us all look at the schematic and maybe we can help.

[blue andry]

hi ,

here it is


this is the first i done schematic ,
please forgive me if i done anything ugly

[blue andry]

schematic link