Hi all,
I am new here, and I joined because I love this forum, pretty competent and friendly techs here
I have an ooooold Carlsbro 60 "plexi" head. Pretty nice end of 60s / early 70s british stuff.
The one you can see here : http://i.ebayimg.com/t/VINTAGE-1968-...)C!~~60_57.JPG it's the same but with original multicolored knobs.
After opening it, according to Chambonino's site, the schematic for this amp is the CS60 BTC, because the two caps from v1 anodes are .047 mustards (otherwise almost the same as a CS60 TC)
Here's the schem : Carlsbro CS60 BTC Amp Schematic
Now, I've got a problem with it. The output is very low, my 10 watts combos are louder.
Everything seems to work fine, I have voltages everywhere, in the correct areas / ranges.
Power tubes
Anode / screen / grid : 460/ 458/ -36
Phase inverter 230v anodes, 30v cathode
preamp tubes 200v anodes (because I swapped the 100k plate loads for 10k resistors to get more dynamic range), 1.3-2v cathodes
Signal caps are not leaky. Fresh power supply and bias caps. Pops everywhere where it should when I test. The amp is ok, as the volume increases with the pot, the EQ is working, as is the "top cut" filter. Preamp tubes ok and tested. Tried with fresh powertubes also. In fact the amp works really well, but has no "Ooommppph" kicking in, no power at all.
I'm suspecting a bad OT.
From center HT to plate windings, I get 80 ohm on one side, 55 on the other. 133ohm plate to plate disconnected.
What is VERY strange in this OT are the secondaries. 9 wires !! 2 black common wires, one single green 16ohm, and two groups of 3 wires for 4 and 8 ohm taps.
There is proof inside the amp there has been output tubes problems, replaced screen resistors, resoldered OT primaries...someone already tested this OT.
Picture of the OT :
So...I would like you to tell me if I missed something. I do not have access to a voltage generator to test the secondaries (maybe a battery?). Any thoughts ?
Thank you very much !
I am new here, and I joined because I love this forum, pretty competent and friendly techs here
I have an ooooold Carlsbro 60 "plexi" head. Pretty nice end of 60s / early 70s british stuff.
The one you can see here : http://i.ebayimg.com/t/VINTAGE-1968-...)C!~~60_57.JPG it's the same but with original multicolored knobs.
After opening it, according to Chambonino's site, the schematic for this amp is the CS60 BTC, because the two caps from v1 anodes are .047 mustards (otherwise almost the same as a CS60 TC)
Here's the schem : Carlsbro CS60 BTC Amp Schematic
Now, I've got a problem with it. The output is very low, my 10 watts combos are louder.
Everything seems to work fine, I have voltages everywhere, in the correct areas / ranges.
Power tubes
Anode / screen / grid : 460/ 458/ -36
Phase inverter 230v anodes, 30v cathode
preamp tubes 200v anodes (because I swapped the 100k plate loads for 10k resistors to get more dynamic range), 1.3-2v cathodes
Signal caps are not leaky. Fresh power supply and bias caps. Pops everywhere where it should when I test. The amp is ok, as the volume increases with the pot, the EQ is working, as is the "top cut" filter. Preamp tubes ok and tested. Tried with fresh powertubes also. In fact the amp works really well, but has no "Ooommppph" kicking in, no power at all.
I'm suspecting a bad OT.
From center HT to plate windings, I get 80 ohm on one side, 55 on the other. 133ohm plate to plate disconnected.
What is VERY strange in this OT are the secondaries. 9 wires !! 2 black common wires, one single green 16ohm, and two groups of 3 wires for 4 and 8 ohm taps.
There is proof inside the amp there has been output tubes problems, replaced screen resistors, resoldered OT primaries...someone already tested this OT.
Picture of the OT :
So...I would like you to tell me if I missed something. I do not have access to a voltage generator to test the secondaries (maybe a battery?). Any thoughts ?
Thank you very much !
Comment