Hello
?? One of my tekkie guys suggested you check the bias at the grids of the PA tubes ( Pull the HV rectifier)... a quick peek at the schematic shows this should be in the -75 or -80 range.
?? The reason we suggested a bias issue is the PA grids are at around -80 which should pretty well keep the PA tubes close to cut-off
? The clamp tube also gets a bias voltage on pin 1 ( I think) and the clamp circuit is set via R30... Consensus here is the issue is a bias problem...
??? We recommend a check of the PA grid components... ( a couple of resistors, a choke)...
??
Ashley
Hi Ashley,
Thanks for the quick reply on my problem!
My low voltage supply is good and my unadjusted bias is -80. I haven¡¯t diddled with that much because I just built a bucking transformer that lowers the line voltage to 111vac but haven¡¯t wired it in yet. I felt the -80 was a bit high but wanted to concentrate on the bigger screen voltage issue. My HV supply is good at near 700vdc and that will come down a bit with the bucking transformer but not 175.
The only thing I haven¡¯t throughly checked is the clamping circuit because I didn¡¯t feel that it wasn¡¯t the main component to drop the screen supply. The manual¡¯s adjustment proceedure for the clamping circuit requires operation of the amp circuit to 230ma. I feel a bit uncomfortable doing that with over 400vdc on the 6146 screens. I would like to get that down before messing up a pair of finals playing with the clamper circuit.
I¡¯ll definitely take a closer look at the clamper components at your recommendation. I did check the clamper tube (and all the rest of them before firing it up on a variac.
Thanks again,
Tom N5AMA
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Thank You
Kiss-Electronics
Ms Ashley Hall
183 N 5th PL.
Cornelius, Oregon
97113
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W7DUZ
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On Tuesday, March 26, 2024 at 05:28:27 PM PDT, Tom Smith <n5ama@...> wrote:
Hi Ashley,
Thanks for the quick reply on my problem!
My low voltage supply is good and my unadjusted bias is -80. I haven¡¯t diddled with that much because I just built a bucking transformer that lowers the line voltage to 111vac but haven¡¯t wired it in yet. I felt the -80 was a bit high but wanted to concentrate on the bigger screen voltage issue. My HV supply is good at near 700vdc and that will come down a bit with the bucking transformer but not 175.
The only thing I haven¡¯t throughly checked is the clamping circuit because I didn¡¯t feel that it wasn¡¯t the main component to drop the screen supply. The manual¡¯s adjustment proceedure for the clamping circuit requires operation of the amp circuit to 230ma. I feel a bit uncomfortable doing that with over 400vdc on the 6146 screens. I would like to get that down before messing up a pair of finals playing with the clamper circuit.
I¡¯ll definitely take a closer look at the clamper components at your recommendation. I did check the clamper tube (and all the rest of them before firing it up on a variac.
Thanks again,
Tom N5AMA
