How to bias a Silvertone 1482

[davohilts]

Hello,
I'm trying to figure out how to bias a Silvertone 1482. The amp just doesn't sound very good and everything else checks out okay. The bass is flabby and distorted and the highs are weak. Thought I'd check the bias to see it it is out of whack and don't really know how to go about it. Any help would be great.
Thanks,
Dave

[booj]

That amp is cathode biased. There is no adjustment. Just measure the voltage at the cathodes to see if it's close to the schematic voltage. Are the tubes good? If they are and the voltage is off, the cathode resistor may have drifted. Probably best to check that anyway.

[gitaar0]

Hello,
I'm trying to figure out how to bias a Silvertone 1482. The amp just doesn't sound very good and everything else checks out okay. The bass is flabby and distorted and the highs are weak. Thought I'd check the bias to see it it is out of whack and don't really know how to go about it. Any help would be great.
Thanks,
Dave

Hi Dave,

It sounds as if you might have to check the powerfilter capacitors. It might solve the distortion and retore some of the highs.

Marc

[davohilts]

The filter caps are new. I just checked the 6x4 rectifier and it was bad on plate one so I found another one and popped it in and that has taken care of the low end issue. The amp still doesn't sound as it should so I'm gonna try and figure out how to check the bias. I'm guessing I measure the voltage on pin 8 of the 6v6's and compare to the spec. My only confusion is how do I accurately measure this voltage, from pin 8 to ground?
I've also heard of a test which measures mV at the output transformer and the negative voltage of the screen but don't feel like I understand that either.

[davohilts]

okay, here is the result of my testing:
Schematic I have calls for 16.8v at the cathode of the 6V6's and I measure 21v on my amp. The voltage changes slightly up and down 1/2 volt because what I am assuming the tremelo circuit not being off just turned down all the way.
The schematic calls for a 270 ohm 5 watt cathode resister and what the amp has is 250 ohm 5 watt.
The schematic calls for 25uf25v cap and what the amp has is a 25uf50v cap.
Any suggestions as to what the heck I should do??
Thanks,
Dave

[JerryP]

One of the first things I would check on an old Silvertone are resistor values. Measure them, they used cheap carbon comp resistors that tend to drift quite a bit over time. Check the plate resistors and power supply resistors to see if they are the correct value when measured. I see these way off all the time. Schematic Heaven shows 2 schematics for the 1482 and one shows 22V on the cathode.
Jerry

[melvin]

You seem to know what it's supposed to sound like, am I right? Those amps always sounded really dark to me. They brighten up if you modify the circuit a bit, at least bypass the first cathode and have a good speaker in it with a proper hole in the baffleboard. Great sounding, light little amps.

[davohilts]

yes they are a little dark but I've put a nice utah alnico speaker in place of the old jenson and that helps quite a bit. The filter caps that replaced the old can are 22uf 500v, 10uf 500v, 8uf 450v. These aren't exactly what the schematic calls for but they seem close. My voltages are low across the board it sees like to me. Primary Voltages off the trans. are 314 vac and the voltages off the filter caps are 341v to the OT, 316v to 6V6's, and 245v to the 12AX7's.
I measured some of the resisters and they are all close except for some of the 330k resisters off the 6v6's which measure 368k and 379k. Don't know really if this means anything.
I'll attach 2 pictures of inside of amp
Thanks

[davohilts]

I've heard many mentions about bypassing cathodes to improve tone. What does this entail? Where is it done. Is it really worth it?

[booj]

I've heard many mentions about bypassing cathodes to improve tone. What does this entail? Where is it done. Is it really worth it?

Fender used 25uf caps, Vox AC30's use a 250uf cap. Bigger cap, more bass response. Makes for a brighter sound with more output. + to the output tube cathodes, - to ground across the cathode resistor. You'd have to try it to see if it's worth it for your own application.

[davohilts]

thanks for the tip, i think i'll give it a try!