Look. This is an amp you dug out of the trash. As you know, you can't make a silk purse out of a sow's ear. I think either concertina or LTP are better than cathodyne. Now which to chose? Pick the one your favorite amp uses. Nobody's opinion will ever help you figure it out. Don't have a favorite? Just roll the dice. It was free after all.
Differential adds an entire extra stage TOO : the right triode is taking signal on the left triode cathode and is working in a common grid mode. Unity gain is obtain by ajusting the common cathode resistance to a high value.
Jacques
I have to say I'm a little disappointed in this forum. I thought it was intended for people to share DIY experiences, and for those still developing to learn from the more well traveled. Some have been helpful (and appreciated), but a surprising number have not.
Being told to go elsewhere and to swot up on other sites, is a little off putting and posses the question: 'what is this site actually for then'? Might just log-out for good.
Being told to go elsewhere and to swot up on other sites, is a little off putting and posses the question: 'what is this site actually for then'? Might just log-out for good.
That's entirely your choice. Here's some tips to help you get a better response if you feel like being a grown up and coming back.
Post in the right forum. You had the option of posting in the Instruments and Amps forum where you would pro ably have got a better response.
Clearly frame your intentions questions, and statements.
If you have already sought advice or tried to get information elsewhere, say so and say why it, wasn't helpful.
Be realistic. We have no idea what your skills are, what your background is, what budget you are working to.
You have presented yourself as someone with a dumpster find wanting a crash course in tube amps for instrumentation so you can modify the amp with little or no thought yourself. That's not the purpose of this forum. You might try Instructibles more your style.
Zebb,
A. There are so many factors contributing to the sound of an amplifier.
Hi Fi amp.
Guitar amp.
How the amp responds to low volume, mid volume, high volume, and at clipping level.
And then . . . there is the loudspeaker you use.
There also is the signal source, a Guitar versus a CD player.
CD players basically sound similar, until you get down to the level of micro dynamics, etc.
Guitars have a much wider range of sound; even one guitar often has several potentiometers and a switch or two.
A single stage of amplification may have varying degrees of distortion.
If it has 2nd harmonic distortion, and the next stage has 2nd harmonic distortion,
there may be some cancellation of the 2nd harmonic distortion.
How one kind of tube stage sounds in one amplifier, as it interacts with all the other stages of the amplifier, can be very different from one amp to another.
A push pull pentode output stage like in your amp, requires negative feedback to get the damping factor to a reasonable level.
Negative feedback tends to hide some of the characteristics that the amplifier would have without that feedback (characteristics other than just the damping factor).
B. Is the amplifier sensitive enough now to use it with your guitar?
If that is so, then . . .
Probably the simplest way to modify your amplifier and get a change of sound, is to do the following:
(This will give less output power, but try it anyway).
1. Remove R15. Replace it with 10k and connect it from that screen to the plate of the same tube (not to the B+ voltage that was connected to the 100 Ohm).
Remove R17, Replace it with 10k and connect from that screen to the plate of that tube
(not to the B+ voltage that was connected to the 100 Ohm).
This becomes Triode Wired Pentodes.
The 10k resistors is a starting point, because the 100 Ohm screen resistors were connected to a lower voltage than the plate. And the plate voltage is too high for the screens.
2. Remove R18, the feedback resistor (that goes from the output transformer secondary back to the input stages cathode circuit, the junction of R7 and R8.
This is an easy mod, and should change the sound, either to your liking, or not.
It is also easy to change back to original.
Now you are ready to listen.
Use it with a CD player.
Use it with your Guitar.
Let me know if you like it.
A. There are so many factors contributing to the sound of an amplifier.
Hi Fi amp.
Guitar amp.
How the amp responds to low volume, mid volume, high volume, and at clipping level.
And then . . . there is the loudspeaker you use.
There also is the signal source, a Guitar versus a CD player.
CD players basically sound similar, until you get down to the level of micro dynamics, etc.
Guitars have a much wider range of sound; even one guitar often has several potentiometers and a switch or two.
A single stage of amplification may have varying degrees of distortion.
If it has 2nd harmonic distortion, and the next stage has 2nd harmonic distortion,
there may be some cancellation of the 2nd harmonic distortion.
How one kind of tube stage sounds in one amplifier, as it interacts with all the other stages of the amplifier, can be very different from one amp to another.
A push pull pentode output stage like in your amp, requires negative feedback to get the damping factor to a reasonable level.
Negative feedback tends to hide some of the characteristics that the amplifier would have without that feedback (characteristics other than just the damping factor).
B. Is the amplifier sensitive enough now to use it with your guitar?
If that is so, then . . .
Probably the simplest way to modify your amplifier and get a change of sound, is to do the following:
(This will give less output power, but try it anyway).
1. Remove R15. Replace it with 10k and connect it from that screen to the plate of the same tube (not to the B+ voltage that was connected to the 100 Ohm).
Remove R17, Replace it with 10k and connect from that screen to the plate of that tube
(not to the B+ voltage that was connected to the 100 Ohm).
This becomes Triode Wired Pentodes.
The 10k resistors is a starting point, because the 100 Ohm screen resistors were connected to a lower voltage than the plate. And the plate voltage is too high for the screens.
2. Remove R18, the feedback resistor (that goes from the output transformer secondary back to the input stages cathode circuit, the junction of R7 and R8.
This is an easy mod, and should change the sound, either to your liking, or not.
It is also easy to change back to original.
Now you are ready to listen.
Use it with a CD player.
Use it with your Guitar.
Let me know if you like it.