Vht pittbull cl50

[DPM309]

I am working on a 2000 Pittbull CL50 amp that sounds flabby, low volume, and distorted. The owner changed all of the tubes and a visual inspection of the board did not reveal anything out of the ordinary. The filter caps looked fine also. From what I can tell on this amp, they use a DC heater supply on the preamp tubes V1, 2, and 3 and AC on the rest. I have had no luck obtaining a schematic since Fryette does not give these out. Here are the voltages I recorded so far. V1, 2 and 3 are for the gain stages and tone controls and V4 is the phase inverter.

Tube P1 P2 P3 P4 P5 P6 P7 P8 P9
V1 ECC83 224 - 1.99 - 12.6 207 - 1.7 6.4
V2 ECC83 259 - 2.0 - 12.6 286 - 3.1 6.4
V3 12AX7 171 - 1.4 - 12.6 357 171 171 6.4
V4 12AX7 214 - 1.8 3.3AC 3.3AC 306 27 104 3.3AC
V5 6L6 - H 429 429 -50 - H - NA
V6 6L6 - H 430 430 -50 - H - NA
V7 5U4GB - - - 356VAC - 370VAC - 430 -

Do these voltages look right? Should the voltages be that high on Pins 7 and 8 on V3 and 4?

Thanks,

Dan

[francy_lab]

Hello Dan,
Also we are working on a CL50 with the problems of distortion, in fact we think that the cause is in power and your reflection was very helpful.
Could you please provide us with a copy of the schematics that you recovered?
Thanks

Frank

[Chuck H]

Hello Dan,
Also we are working on a CL50 with the problems of distortion, in fact we think that the cause is in power and your reflection was very helpful.
Could you please provide us with a copy of the schematics that you recovered?
Thanks

Frank

He said that he DOESN'T have a schematic.

[Chuck H]

Dan, it's an intuitive game to interpret voltages without a schematic. Nothing in the voltages posted looks "wrong". This assumes the amp is using a cathode follower for V3b and the PI is a cathodyne. One note would be that on V3b, if it is a cathode follower, the voltages for the grid should be lower than the cathode by a volt or two. This could have been easily overlooked when ball parking voltages for posting or even if the meter reading wobbles a little for any of a number of reasons.

Considering the design I think it's possible that the flabby tone is inherent to the amp. It may be that the owner found a need to turn the amp up loud, and hadn't before under high drive levels, and the cathodyne inverter or speaker response is misbehaving. Even if the owner says the problem wasn't there before I think there is still the possibility of a misrepresentation on their part. It's the cynic in me If the amp is clearly misbehaving then perhaps it IS broken. Maybe not. With that much drive in the preamp and a cathodyne inverter I wouldn't expect the amp to NOT be flabby when driven hard. It would be odd if it weren't. In which case it's behaving correctly.

EDIT: I forgot to address the "low volume" issue. It's easy enough to check the watts. I would expect about 45 to 50 watts from it. If it's below that then perhaps there's a problem. Otherwise it could be that the owner needed to turn it up and it wasn't loud enough. It's often surprising for the uninitiated when an amp they thought was loud at practice or at home is suddenly weak and feeble in a large room or on an outdoor stage with a drummer at their back.