Tube Amp Archive

My previous thread.. https://tubeamparchive.com/viewtopic.php?t=12110&highlight=hum I have done a couple of things to try and fix this hum problem. #1 I took out my input selector switch and I took out the hum balance pot so everything is original to specifications. The next thing I did I went to t...

Could be a ceiling fan speed control.

This I what I'm thinking

How exactly could drop the voltage with a zener diode? Which one do I use? Where exactly do I place it?

What is the voltage on your cathode now?

jcat5503 wrote:Okay here's my voltages:

V1 EF86:
1 - 93
6 - 191

V2 12AX7:
1 - 260
6 - 270

V3 El84:
7 - 361
9 - 371

V4 EL84:
7 - 363
9 - 371

Any thoughts?

Cathode voltage?

What value is your cathode bias resistor? It's 120 ohm, I'm wondering if I need to increase it I will check the plate here in a few I just got a new set of 84's to see if the higher voltage killed them in a short amount of time and that's what is causing all the problems I'm betting your plate volt...

You can totally use a 5Y3 with a pair of EL84's. Of course, if that's it. Not familiar with the amp so as I said, if the amp was designed to "need" a GZ34... Also since the voltage drop of a 5Y3 is about 40v more than the GZ34, there will be a lower rectified voltage to partially compensate for the...

Nik uses a 290-0-290 PT and a GZ34, and I used a 330-0-330 PT with a 5Y3 An amp designed to need a GZ34 cannot use a 5Y3. The current handling capacity of a 5Y3 is only half of a GZ34. Since your PT is sending higher B+ you are probably over driving the EL84s and overloading the 5Y3. I'm suprised y...

Just wondering if a ham&egg tech, like me, can determine if an amp is truly operating in Class A, without the use of an oscilliscope ? If there is a thread on this subject, from previous discussions, that would be fine. Thanks, Art It's not mysterious. First, decide if your amp has a "single ended"...

Any progress?

Your factory diagram specifies a 5U4 but the hand drawn PS shows a 5Y3 and a 300R resistor ahead of the first filter. Are you still working with a 5Y3 and the modified input components? Your 5Y3 is only good for half the current of a 5U4.

That may be a tranny from an Electro-Voice A20C. Potted, light color paint?

If so, it used 6v6 tubes, PP.

Secondly, I measured the resistance to the primary of the power transformer and I get 2.6 ohms. The wiring diagram shows it should be 17.5 ohms. So I'm wondering if I have a bad power transformer. Look closely at diagram for the primary resistance. Could it be 1.75 ohms? That is more likely for a p...

100 ohm 4 watt wire wound pot for hum adjustment

Why did you change the original heater circuit from a 100R/100R balanced centertap to ground to a 100R pot? Don't modify anything until you have a working original circuit. The original unit didn't hum when it came from the factory.

I received a large number/variety of 1/2 watt metal film resistor for an amp I'm building, and ALL are the same physical size EXCEPT the 100K's, which are about half the size. I think these 100K's may be 1/4 watt, given the size difference, but how does one know ? I don't know if they all come from...

On the data sheet for the Stealth diode is says: The soft recovery minimizes ringing, expanding the range of conditions under which the diode may be operated without the use of additional snubber circuitry. So is the noise associated with SS diodes more properly called ringing? Yes, but don't lump ...