TapeMaster SA-13 Chop-n-bob.

[DummyLoad]

Tapemaster SA-13 stand alone mono reel-2-reel amp, SE UL mode with a 5881. Rare beast, can't seem to find much info on it. Appears to have been worked on, at least the power amp stage seems that way - THe plate and screen tap leads were spliced. The rest seemed to be untouched. Schemas attached and link to project pics. Odd NFB stuffs happening on the output stage and NFB taps to the driver as well, looks like the Hammond FR40 amp plans, only this is SE not P-P. I reverse engineered it, so original and mod schemas are attached.

With guitar and amp dimed, the output was anemic, so I punched out the 1st amp (7pin 6C4) to accept a 9pin noval socket to accommodate a 12AX7/AU7/AT7. I also added a 4th RC filter for the 12Ax7 1st gain stage. To keep it relatively clean, I installed a 12AU7 as the owner wanted clean as 8 watts can get.

Also, I experimented with a 12AX7 and very pleasing overdrive with compression resulted, lots of usable feedback if guitar and amp were dialed in. Yes, now it looks Ampeg B-15-ish preamp to UL SE output stage. No mods were made to output stage other then the NFB was reduced to the driver amp.   
 
Enjoy!

--Pete

https://www.dropbox.com/scl/fo/szd18d4v0sjhul73o1kcq/h?dl=0&rlkey=uwq99qmlhggeqt2flnp8r3kbz

[Latole]

Pictures;

[rybcage]

I’m so pleased that you posted this info about the Tapemaster SA-13 amp. I have been searching for any useful info for years. I got one of these some time ago that someone had started to repair or modify and left undone. I am hoping to put it back into operating condition as a small guitar amp but I am an amateur, still learning about how tube amps work. I know enough to replace existing components but not how to analyze the circuit to determine what might have been removed without good documentation. It is such a classic looking little amp that appears to have a lot of promise.
If you have any more pics of the before and after mods it might be helpful to me.

[DummyLoad]

If you have any more pics of the before and after mods it might be helpful to me.

The first 9 shots of 19 in that dropbox link in the opening post are before modifications, the remaining 10 are after. Sorry, but the shots in that link are all I took. They were detailed enough for me to to draft most of schematic. As for the repairs, it was in dire need of a cap job + cold solder joints on the 5881 had it flying off into ultrasonic oscillation.

Need to note that it looked like the amp had been serviced previously, however, I do believe that it was simply a repair job but that's speculation.

There is an error both before and after schematics: V4, 5Y3GT, B+ tap is from pin 2 and not pin 8 as depicted in the schematics.

--Pete

[kagliostro]

Ciao Pete

Very nice looking old amp 👍👍👍

Which Is the material that firms on place the grillcloth ?

Thanks

Franco

[JPK]

Looks pretty normal until you get to the OT. Is that a p-p OT (wired SE)? Cool project.

[kagliostro]

That Is an UL OT

Ultra Linear Output Transformer

Franco

[JPK]

That Is an UL OT

Ultra Linear Output Transformer

Franco

Cool stuff. If I keep hanging around here I'm gonna lurn somthen.   

[DummyLoad]

Which Is the material that firms on place the grillcloth ?

K, I think it is particle board.

The chassis layout sucks - Has the PT on the same side of the chassis as the Input jack, presume why the sheet-metal shield was put in front of the input jack. The neutral line is fed to the power switch located on the volume control, so that helps. I does hum and is was much more  pronounced if I used a 12AX7 for V1, however, with the 12AU7 installed it's fine. 

Very nice looking old amp 👍👍👍

Thanks K! Hope you are all doing well. 

--Pete

[Latole]

Which Is the material that firms on place the grillcloth ?

K, I think it is particle board.

--Pete

That's exactly what I think, but I figured it must be the effect of the recovering / tolex, no one would make a cabinet by leaving particle board visible.

[kagliostro]

Thanks Pete

Doing .... Better don't talk about 😁


Franco

[rybcage]

I thought you might find this trivia of interest. I found this old ad for the original tape recorder and this auxiliary amp/speaker combo that I found interesting. This was about all I could find prior to your posting of this project. It’s from a copy of Audio Engineering Aug 1952 I found on World Radio History site.
It originally cost about $80 which sounds pretty cheap but
$80 in 1952 is equivalent in purchasing power to about $841.67 in 2022. Of course that was for brand new condition, not a 70 year old nonfunctional amp with misc parts missing.

https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/50s/Audio-1952-Aug.pdf

[rybcage]

This got me motivated to get back to working on my SA-13 amp. Looking at it I just realized mine is a different version than yours. Mine has two 6C4 tubes rather than the one that yours originally had.
Here is a pic of the top with the sockets labeled.
I wish I could find a schematic for it. I don’t have enough experience to generate my own schematic.

[rybcage]

Here’s the insides. It’s a bit different than your amp also.

[DummyLoad]

Here’s the insides. It’s a bit different than your amp also.

Other than the added choke and butcher job on the power supply, the rest of it looks quite similar. Someone butchered the PS, Looks like the 400Ω 10W resistor was replaced with a choke? There seems to be cap(s) missing in the power supply. Did you get the amp this way?

Respectfully,

--Pete

[rybcage]

Yeah, that’s pretty much what it looked like when I got it. As I recall I only ended up having to pay a small amount for shipping it was otherwise free so how could I resist? I had hoped I’d be able to make a low watt guitar amp out of it but its a bit over my head, at least for now.

[rybcage]

I showed it to a local tube amp repair guy I recently met and he suggested it might be worth rebuilding it into a Champ which is kind of what I was originally thinking this amp might lend itself to. It’s such a cool looking little amp with beautiful transformers and faceplate. This will be new territory for me. I have never built an amp. I’ve done some repair of vintage amps by simply replacing caps and resistors that had gone bad. Building a tube amp from scratch will be a new challenge that I’m considering.