The Amp Garage

The cathode resistor Rk and anode load resistor Ra, along with the supply voltage, determine the operating point, and the cathode resistor bypass capacitor Ck determines frequency response at the low end. Right now both stages are using 100k Ra and 1k5 Rk, center-biased and fully-bypassed with a 22...

The layout could be modified to correct the issues that have been mentioned here. You could also play around with the operating points on the preamp tubes to get a feel for how that works. When you say change the operating points of the preamp tube, are you referring to changing the bias? If so, wo...

The caps are probably easy to get to, and there aren't more than ten BIG solder connections. This is not tiny underboard work on amps of that era. I could be wrong. Do you have a gut shot of your amp? EL caps are seriously easy and we can talk you step by step. You only need a table top, a general ...

The caps are probably easy to get to, and there aren't more than ten BIG solder connections. This is not tiny underboard work on amps of that era. I could be wrong. Do you have a gut shot of your amp? EL caps are seriously easy and we can talk you step by step. You only need a table top, a general ...

I got sidetracked from my post here, but I'm still wanting to get the amp fixed and finally pulled the chassis this morning. I've been referencing the schematic and guts to get a list of all electrolytic caps that would need to be replaced. When I went to pull the chassis, though, I noticed somethin...

So what’s the reason you can’t jump a scrap of wire across them, just tin the wire once you strip it. you can even give up a spare cap or resistor and cut a lead off of one of those to span the two terminals. I'm probably missing something, but aren't the two tips on that type of jack only supposed...

I don't think there was anything wrong with the kit. Switchcraft jacks are generally of good quality, but occasionally have this problem. I would fault the instructions for not being clear on the need to remove the paint from the contact surfaces, and the layout is not the best, IMO, and could be i...

Try bending the contacts with a chopstick or something that you can use to put pressure on them close to the jack body. Some needle nose pliers seemed to do the trick (after draining the filter caps). I guess I'll just have to see how it holds up after using the jack a few times. But with that fix ...

Is the shorting contact making a good connection to the long tip contact? If that is not happening you will get hum since the input is open with a 1 Meg impedance to ground. Sometimes you have to bend the shorting contact a bit or clean the contact points. An intermittent contact with the plug is n...

I measured the AC voltage across the speaker jack and got a max value of about 3.5vac, but it seemed to hover around 2.0vac which is consistent with the kit guide/schematic. That 2.0VAC reading is supposed to be under the conditions detailed at the upper left of the schematic. You set the Volume co...

It does. The reason the manual probably doesn't mention it is assuming the builder doesn't have probes that clip on, and putting both hands inside the chassis is a potentially fatal maneuver. You have to be very careful when you do this. It will give you the voltage the heater actually sees though ...

I wasn't sure which you meant, but I tried reconnecting the wire on the jack sleeve lug that goes to the volume pot and instead connected it to the grounding lug for V1 pin 3 (which I believe is where the cathode is grounded). This actually made things worse. The buzz was still there with the volum...

Are you sure the input Jack has a good ground? What happens if you connect the sleeve lug of the Jack to the ground lug where the first triode’s cathode is grounded? Do you mean undo the connection that's currently running from the input jack sleeve lug to the volume pot, and then make a new connec...

One could expect some buzz from ripple voltage on the B+ in a single ended amp, so another interesting measurement would be the AC voltage at the speaker with the preamp tube removed. It was previously stated that the hum disappeared when the preamp tube was removed, so I concluded that the issue w...

...what do you mean by checking the tube pin to pin? Would this mean connecting both probes of the meter to tube pins? It does. The reason the manual probably doesn't mention it is assuming the builder doesn't have probes that clip on, and putting both hands inside the chassis is a potentially fata...