Help Needed with a 1963 Teisco 74R Tube Head

[Udonitron]

OK guys need your advice etc on this amp I just picked up
1st time thread for me here, new member
Rare bird, only three can be found via a search on the net and not much info at all on the 74R's.
Notice how the previous owner has wired up 2 plugs one off the small toroidal output transformer and one off the power transformer?
The huge round one was added later to replace the stock dead one at some point I assume?

Amp noob here but perhaps one of you guru's could give me some insight into this amp's wiring etc?
The brown wire from the output was cut and attached to the red off a different pin as well
Sorry for the crappy blurry pics

TUBES:
2 x 6V6GT
1 x 6SN7GT
1 x 5Y3GT (rectifier)
6 x 6AU6A

Where to start to get this up and running minus getting tubes for it?
Amp tech perhaps but any advice or knowledge would be great as I am hoping to start doing some rebuilding on a few old Japanese amps I have.
Cheers in advance for any and all help!

[Udonitron]

[Udonitron]

Last set here:

[sgelectric]

Hi, I just stumbled on this post. Have you been able to sort out this amp yet?..Looks cool in a funky sort of way
The OT in your amp is almost certainly non-original......Sansui made some excellent Hi Fi transformers in the years before their switch to solid state.I don't think Teisco was working a price point that would have made the Sansui OT a viable option....Goggle "Sansui in the early years" if you're interested.
The small *toroidal* transformer which you referred to may in fact be a non-toroidal reverb transformer......... Hope all is going well with your project
SG

[Udonitron]

Hey SG

Sweet, thanks for the reply
I have not done anything with it yet other than getting tube for it.
Have yet to power it on as I have to volt meter the caps to see which are shot and which are not.
I have 2 Ace Tone's and a Guyatone I am currently trying to rebuild but with Canada Post on strike, everything is delayed
Perhaps I can pick your brain when it is time?
Makes sense about the reverb tranny!!
Glad to head the OT is a higher end one, whoever owned it before me had some idea obviously

Cheers!

[riz]

I think that is a cool looking amp, love the RED chassis!! To my eyes a very artistic point-to-point build. I notice they've got an unused punch there for a cap can or a tube socket...

[sgelectric]

Hi, Questions,question, questions

Is the reverb tank still in the head cabinet?......
Are there two small speakers in the cabinet? If so,who made them and what is their nominal impedance ?
Is it possible that some of those 6AU6s might be 6AV6s?
Do you know if the transformers are OK?

It would probably be a good idea to replace all the electrolytic caps in the amp
I notice the replacement transformer is spec'd at 5000 ohms impedance, a bit lower than what one commonly sees for 6V6s (6.6k-10k).While it may run fine at 5k, it is also very easy to run it at 10k by carefully selecting which speaker output you use.Just an option.
Later, SG

[Udonitron]

No it used to be a 4 x 6" combo but the previous owner tuned it into a head.

Like this one:



Regarding the 6AU6, sure they could have been AV6's as well but are they not very close?
Have not tested the tranny's but I can for sure.
I need to get some 6V6's now, all other tubes are bought.
Caps for sure will be replaced.
By speaker output are you referring to the ohms or wattage?

Cheers man

[sgelectric]

Regarding your 6av6/6au6 question : They are not very close and are definitely not compatible.The first is a triode/duplex diode and the second a sharp cut-off pentode.I only asked because Teisco used 6av6s in some other models.

My question about the speakers referred to ohms.............SG

[Udonitron]

Mmmm from all the reading I did on it I understood the "6AT6 has a u=70 and the 6AV6 has a u=100" but they are interchangeable other than a gain difference?

4 of the 6 small tube inputs have the original 6AU6A's in them...only 2 are missing so I assumed they were all 6AU6A's

[Udonitron]

Ah nice...check this...so there are 2 6AV6's then!
I have a few NOS's at home I think.
Forgot I had posted in that thread too but no replies

http://music-electronics-forum.com/t1416/

Here are the specs:

Tube compliment: 4 each 6AU6, 2 each 6AV6, 1 6SN7GT, 2 each 6V6GT, 1 5Y3GT

Instrument Input Jacks: 2 "Normal," 1 "Treble"

Controls (Left to Right): (1) Depth (2) Speed (1 and 2 for Tremolo) (3) Echo Depth (4) Volume (5) Bass (6) Treble

Additional front panel jacks for "Tremo Pedal" and "Echo Pedal"

Speakers: 4 total, approximately 6" each, wired in parallel to a single output transformer.

[sgelectric]

The 6AT6 and the 6AV6 can be be swapped depending on the amount of gain one wants.I doubt that the diodes are used in this circuit.Note that they have the same pin-out.
The 6AU6 is a totally different type with a different pin-out.Don't let the fact that the letters in the code seem close/similar lead you to assume anything between two tubes.Check the book if you are not completely sure.
I'm getting the feeling that you may have to resort to drawing your own schematic as one does not seem readily available.You already know the rectifier and power tubes.Judging by the position of the fourth octal tube socket,I'd assume the 6SN7 is your PI........and so on.It's actually a very instructive process.Good luck SG

[tominokinawa]

Hi, I have the combo version of this amp. If you change the power tubes is the amp self biasing. If not how would you bias it?