Can you identify this Teisco tube amp?

[ian2113]

Hello,

I've just finished servicing a mid-60s Teisco tube amp for my brother, and I would like to find out more about it. (A model number might help me find a schematic, for instance!)

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.

Covering is a swirly reddish-purple with sparkles, similar to the covering on the Teisco 78-R shown on Larry McNally's Teisco amp website. (I've sent photos to Mr. McNally and he hadn't seen this particular model before.)

Anyway, I would appreciate hearing from anybody who may recognize this old Teisco, from anybody who might have a schematic, and *especially* from anybody who might have another one they'd like to sell!

Thanks for looking and reading!

Cheers,

Ian Abbott

[tonga]

Hi,
The amp I got here looks very similar to the one above.
I've attached a photo, I have no information on it though, no paper work or documentation of any kind, sorry!
I was hoping you might have some info by now.
Thanks,
Craig

[ddc53]

if you still have the teisco 74R

I have a question for you. I bought the same amp a few months ago and the person that sent it to me did not mark which pre-amp tubes went where.
since they are all the same size and actually do work in several configurations...I would greatly appreciate it if you could posibly let me know the correct configuration as i can not find info. anywhere. Thanks, dc

[Udonitron]

Hey DC

Digging this thread up only because I just got one of these yesterday from Japan but it is the head version
Never seen the head only version before.
It is a Teisco 74R
The tubes are as follows with the sockets closest to you left to right:

2 x 6V6GT -> 1 x 6SN7GT -> 1 x 5Y3GT (rectifier) then all the tubes to the very right are the 6AU6A's (but mine has 6 of those, not 4?)

I will post pics as I think the previous owner did some crazy mods as it has one hell of a huge round transformer on it

[Udonitron]

OK guys...here are a few pics.
Notice how he has wired up 2 plugs!?
Why are both the output transformers wired...how in the hell does that work?
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, it was a little dark so the shutter was delayed.
Cheers!

[Randall]

Yep. Pretty sure that's the one my friend has. Sounds great! But so far no luck at all finding any info. Even has the same green wire for everything.

[Udonitron]

Yep. Pretty sure that's the one my friend has. Sounds great! But so far no luck at all finding any info. Even has the same green wire for everything.

Do my a solid mate and take somepics of his wiring so I can use that as a proper schematic
Also see what tubes are in the pre-amp there.
I am missing a few and wonder if they are all 6AU6A's?
Cheers!

[Gingertube]

I had a Tiesco 78R which I did a restoration on for my niece Laura when she joined her first high school band. I did a full circuit trace of it at the time. 6AV6 preamp tubes, 6SN7 and 6L6 in the power amp, 5AR4 rectifier. It had all green wire too.

Away from home for work at the moment- will do a search for the circuit trace when I get back next week.

Preamp tubes are all 6AV6 which is a high mu single triode with identical specs to 1/2 of a 12AX7. It also has 2 diode plates in it which are just left unconnected.

http://www.tubebooks.org/tubedata/HB...art_1/6AV6.PDF

Cheers,
Ian

The 6SN7 is a cathode follower to drive the output tubes.

[Udonitron]

Hey Ian

Awesome!
Please do keep me posted, it will help big time!

Cheers
Chris

[Gingertube]

Hey Ian

Awesome!
Please do keep me posted, it will help big time!

Cheers
Chris

Better late than never - cleaning up the workshop on the weekend and found the Tiesco 78R schematic trace. The old brain ticked over and accused me of "promising these to someone". So a quick search.

I'm fairly sure there are 1 or 2 errors in the trace but it may help.

Cheers,
Ian

[Gingertube]

In a post further up I said that the 6SN7 was used as cathode followers to drive the output tubes. From the schematic trace (sht3) you can see that this is not the case, the 2 triode sections are arranged as a simple differential driver. The power amp section is basically the Williamson HiFi Amp design scheme. Concertina Splitter (12AU7) into a diffamp driver (6SN7). Why they did'nt use 12AU7 for both or 6SN7 for both (since they are almost identical performance/specifications tubes) I could'nt even guess.

The bit of the trace I think might be wrong is the 10uF cathode bypass cap on V9 (Sheet1). I can't see how the tremlo would work with that cap in place. It would simply short the modulation signal from the cathode of V8 (Sheet3). So I'm convinced that that cap does not exist and I was getting confused with one of the other tubes when I traced the circuit.

Cheers,
Ian