Are all phase inverter arrangements compatible with all output tubes?

[akimball442]

I have a Blues JR amp that has more problems than it's worth, so I've gutted out the amp completely. I installed conventional tube sockets and an eyelet board. The new circuit does not even resemble that of the Blues JR.

Here is the circuit:



Some of you may recognize it from a previous post that I did earlier with different questions. This amp built in it's original chassis sounded quite good (but there's always room for improvement, right?)

As much as I have learned, I only have a very limited knowledge about phase inverters, and I'm not sure how to even name this one.

My question is basically this: Will any phase inverter arrangement be compatible with any output tubes?

This amp uses the strange (and very nice sounding) 6973 output tubes. They have a very unique distortion character, and I really like them.

Since this is experimental, I'd like to try a few different things. My first thought is to use the front end of a 5E3 Fender Deluxe.

http://schematicheaven.com/fenderamp..._5e3_schem.pdf

If I build the Deluxe schematic through the phase inverter, what, if any changes would need to be made in order to have it be compatible?

The reason I'm not just jumping into this is because There are several different amplifiers (particularly cheap Valco made models in the 60s) that use the 6973 output tubes, and none of them are using the type of phase inverter in the Fender circuit.

I guess basically the question is, can I build the Deluxe circuit using the 6973 output tubes instead of the 6V6 output tubes, with the correct OPT and bias?

[JHow]

I'm not the guy to answer all your questions, but it looks like paraphase inverter to me. That scan is really small and hard on the eyes. What is the original amp?

I think, in theory, you can change the preamp, or power amp to go with the inverter section - assuming you take into consideration power requirements, voltages, etc., but this will likely require a lot of planning on your part first.

[Wilder Amplification]

I'm not the guy to answer all your questions, but it looks like paraphase inverter to me. That scan is really small and hard on the eyes. What is the original amp?

I think, in theory, you can change the preamp, or power amp to go with the inverter section - assuming you take into consideration power requirements, voltages, etc., but this will likely require a lot of planning on your part first.

1/2 right...it's a floating paraphase.

The only time a power valve type would govern which type of phase inverter to use would be if the power valves required a minimum amount of grid drive to swing to max power that say a unity gain phase inverter couldn't supply. But even then you could use a cathodyne style PI circuit and place another gain stage after each side of it to increase the grid drive if need be.

[akimball442]

Apologies for the small drawing! I have the original and it's quite large. I actually photographed it from inside of the cabinet where it lives. I'd be happy to upload it some other way, I've been using photobucket, but it seems they reduce the size of the photo automatically.

The original amplifier was for a portable RCA PA system, which was mounted in a cheezy enclosure bearing a 6" Jensen. The construction of the chassis and the iron used are first rate, though. And I don't think this thing had been turned on twice since it was built in 1960. My father works for a college, and they were throwing it in the garbage. He rescues some of the coolest stuff for me...

Thanks for the replies. Rather than waste time with silly newb questions, I'll search around and try to learn a thing or two about the differences between each type of phase inverter, as I suspect it's been covered before. If not, I'm basically interested in the pros and cons of each type, assuming that it's not all just a matter of 'more than one way to skin a cat'.

Aaron

[JHow]

1/2 right...it's a floating paraphase

I get it now. I took more time to follow it out. Thanks for pointing it out. I like these discussions where people re-purpose these old PA amps. I guess I need to spend more time at the garbage bins of local education establishments - I never see this stuff.

[Wilder Amplification]

Apologies for the small drawing! I have the original and it's quite large. I actually photographed it from inside of the cabinet where it lives. I'd be happy to upload it some other way, I've been using photobucket, but it seems they reduce the size of the photo automatically.

The original amplifier was for a portable RCA PA system, which was mounted in a cheezy enclosure bearing a 6" Jensen. The construction of the chassis and the iron used are first rate, though. And I don't think this thing had been turned on twice since it was built in 1960. My father works for a college, and they were throwing it in the garbage. He rescues some of the coolest stuff for me...

Thanks for the replies. Rather than waste time with silly newb questions, I'll search around and try to learn a thing or two about the differences between each type of phase inverter, as I suspect it's been covered before. If not, I'm basically interested in the pros and cons of each type, assuming that it's not all just a matter of 'more than one way to skin a cat'.

Aaron

Everything you ever wanted to know about phase inverters -

Valve Wizard - How to design valve guitar amplifiers

Scroll down and on the left you'll see links talking about paraphase, floating paraphase, cathodyne, AC coupled long tailed pair, etc etc.

[Steve Conner]

Well, looking at the 6973 datasheet:
http://www.jogis-roehrenbude.de/Roeh.../6973/6973.pdf

It seems to need just about the same amount of grid voltage as a 6V6 to do its thing.

And as Wilder points out, that's the main issue: if you take some power tubes that need lots of grid drive, say 6L6s, and hook them up to a PI that can't provide much, say a cathodyne, then you won't get the full output power the tubes are capable of, and the results will generally be a bit rubbish.

But neither the 6V6 nor the 6973 needs much drive, so I think the 5E3 plan would work fine.

Dumpster diving at colleges is great fun. Better yet, just get friendly with the technicians in the EE department and ask if there's any old tube junk you can have. I got 7 GEC KT88s this way. They're not matched, but beggars can't be choosers.