Got this off the bay awhile back, just getting to it now.

Seller pics.

The seller said the reverb does not work and I found the tank output coil to be broken.
No surprise, considering the amount of corrosion in there... 

The schematic inside the back panel is "not quite" correct.

I traced the board and drew a correct schematic. (next post) 

Does anyone use tube shields on EL-84's?

I've been working on this amp and noticed that the EL-84's seem to radiate a LOT more heat than the 12AX7's.

It's seems like the heaters in the EL-84's get very hot compared to the 12AX7's

Before noticing this extra heat, I saw some extra tall tube shields that will fit the EL-84's.

So I ordered some thinking to use them more for tube retention than shielding.

I'm concerned that they may trap the heat and shorten tube life.
Am I way off base here? Will it matter at all?

I know there are wire tube retainers for these tall 9 pin tubes,
but the amp has those bases made for shields just like the 12AX7 tube and I thought to put them to use.

AFAIK this amp never had retainers at all for the EL-84's.

Should I even bother?

I'm working on a Traynor Guitar Mate III that seems to be from 1969-1973 era.

I'd like to pin it down a little closer...

On the pots...

It has Centralab very clearly marked on the front bushing, but the codes on the back confuse me.

Did some googling to no avail...

On back of the vol pot is...    4482  1MEG-A  *then* BD7Q-7  OR   8070-7

The 1MEG-A is easy, the rest...?

The BD7Q or 8070 is hard to read, I'm guessing it's 8070.

The Centralab manufacturer number should be 134 but it's not there...?

Thanks for any help.

Edit; hmmm   8070   8th week of 1970? but why the dash 7?

Here's a schematic and layout for the Unicord Stage 65 amp. 
Took me some time to draw this...

I found this on ebay as just the chassis, no cabinet.
Will post more later about this amp and mods I did to it.

I picked this up about a year ago. Finally got to looking at it.

Made by Mirtone in Weston Ontario, Canada.
Info on these seems to be non-existent. No schematics, nada.
Only thing I found was some other person looking for info too.

The only date code I found so-far seems to be 1966, so mid 60's design.
All germanium negative supply. -46V rail.
It is quite loud tho I doubt 100 watts.

Does not seem to have anything in common with the USA made Silvertone 100.
Those have a printed circuit board, this one, not at all.

Has nice compression/crunch at full volume.
The reverb sounds like ass. Very artificial metallic clank noise.

Did the usual 3 wire cord and clipped death cap.
Added a fuse holder as there seemed to never have been one!

It's quite noisy (hissing/rushing noise) but I'm waiting for the 3 can caps to see it that helps.
Temp jumpered up a big cap to the main cap can and the noise got a little less, so we'll see.

Already replaced all other small electros, what a pain point to point terminal strip wiring is!
Very robust construction but a dog for repairs and making changes,
unless you just clip the part and tack on a new one. Not my idea of the right way to do it.

The Mirtone model # is hard to read, says GA-100.

Reverb tank held with failing double sticky tape so I bolted it in with some rubber grommets.

I never thought I'd see another one of these! 
This is exactly like the very first amp I had in the early 70's.

Made in Japan, it is exactly like many of these "Mini Stack" amps that usually came with a 2X8 speaker cab.
I own a few of these, Teisco, Audition, Kingston, Domino, plus I've seen some with other names, some with a 1X12 speaker in the same size cab like the Wabash.

This Sears did not come with a speaker cab, but I have a spare cab that I found on Reverb.

They all have the input jacks on the right, with the exception of the Teisco.
Circuits are not all the same, but there only seems to be 2 different ones.

I picked up this Hohner 12R on ebay.
Thought it looked cool and it was cheap. 

When it got here it was damaged in shipping, 
and I ended up getting a full refund including the shipping. 

Pulled the chassis out, with the idea that I might repair the cabinet or make a new one.
The amp still worked and didn't sound half bad.

With the chassis out of the cab I found "Marlboro" etched on the circuit board and Marlboro branded TO-3 output transistors.
A little research an it seems Marlboro Sound Works made many amps that were re-branded,
Hohner
Paramount
and probably others.

Looking at the chassis on my bench... ideas began to form... and I abandoned the idea of fixing the cabinet....

More to come later.... 

New Amp Day!

Look what landed on my doorstep today!

Thought I'd put this here since its a tube amp. 

Found this on Reverb for a good price.
It sounds great considering the speaker cone is a little soft. Farts a bit on low notes.
Speaker looks original, as do the tubes.
The 6X4 rectifier is a JAN Phillips, not sure if that would be original.

Is that really how they hooked up the speaker back then?
Right off the O/T winding?

When I got this it kinda worked, but both treble controls were broken.
The knobs would just spin and no change to the highs.
Both treble control pots have a "pull brite" function.

Nice that they used CTS pots as I have found that you can take them apart and swap parts or repair as needed. 

As I suspected the plastic carrier for the pot wiper was broken so it was just a matter to swap in a good one.

I also changed out all the electrolytic caps including the big-ass main filters.
These caps are all from around the early 70's and the amp had some noise issues and some "fuzzyness" to the sound.

All cap replaced with same values except for those big-ass filters.
The originals were 7000uf and all I could find to fit the holding clamps were 10,000uf units.
Well... I could have fit even bigger but thought the 10,000 was enough. 

Someone had already installed a 3 wire power cord,
I finished the job by clipping out the line reverse death cap.

After all repairs it is very clean and VERY LOUD!
Even at full volume thru a 1X12 cab Celestion G12H there is no hint of distortion at all.

I haven't tried any pedals in front of it yet.

TEISCO CHECKMATE 25 SS HEAD
REPORT AND RESTORATION
[Or, how to polish a turd]

Sorry for the long post. 

I found this amp on eBay, cheap.
No matching speaker cab, but there is one of these amps on Reverb(dot)com with the speaker cab, so I grabbed the pictures so you can see what it looks like.

The seller of this one said... "Its old and it works"...
So when it got here I plugged it in and it did "work".

Very quiet barely even bedroom volume level.

The tremolo works, a bit fast on the speed range though.

The reverb is a very UN-musical clank!

Opened it up to find disgusting mess of dead bugs, cobwebs and general filth.
Cleaned the mess and added a 3 wire power cord and got rid of the death cap.

The Voice channel has the highs rolled off, very dull sounding with guitar.
47nf cap to ground, right on the Voice volume control.
(I assume Voice means Microphone input)

Taking a quick look at the boards I noticed an abundance of 10uf electro caps that appear to be used as audio path coupling caps.
I don't like electrolytic caps in the signal path so thought I'd replace them with 1uf box film caps.

I'd need a schem to do that....
(Well, I could do it without a schem, but I'm gonna draw one anyways)

However, the input cap C1 right after the jacks was easy to spot without a schematic so I replaced that one first.

Holy Hanna!
After changing just that one cap this thing got very LOUD!
(Relatively speaking)
Driving a Jensen MOD 10-50 speaker.
Changing that one cap convinced me to re-cap the whole amp.

So did that, and replaced the trimmer TR1 100K in the power amp.
The original open frame trimmer was kinda glitchy and rough looking.
Installed a better quality Bourns sealed trimmer.
With a volt meter on the output junction between Q5 and Q6 I adjusted the trimmer for ~ half the supply voltage after warm up.

Amp sounding "not bad" now, but the reverb was still that gawd-awful clank sound.

What to do....

Noticed the tank was installed backwards...
Input was marked on the tank, and input was connected to the recovery side of the circuit.
Switched it around and.... No difference....

Opened the tank and noticed it's a piezo type. Ah-ha.
Likely makes no difference which way it's hooked up.

Hmmmm,
The cabinet seemed big enough to install a "normal" full size reverb tank on the inside top.

Have such a tank in my junk and determined that it would fit.

The tank I have has the often used 8 ohm input impedance common in many tube amps.
Did some reading/research and found that this can be difficult to drive.
Connected it to the existing circuit anyway, just to test and... no reverb sounds.

Rattling the springs/tank produced reverb noises, so the recovery side will "probably" work ok.

Well, reverb tanks are relatively cheap so ordered up a 4FB2A1A.

4= Type 4 - 17" long, 4 springs
F= 1475 input impedance
B= 2250 output impedance
2= Medium decay
A= input/output grounded
1= No lock
A= horizontal mount, open side up

So the higher input impedance of the new tank should be good... at least easier to drive...

Connected this new tank directly to the existing circuit, knowing full well that it probably would not work.

Nope, gonna need a drive circuit.
What to do....

I lifted the reverb drive circuit almost verbatim from a Univox U65G schematic that I have. I even have a spare 2SC1317 transistor!

The Univox reverb sounds ok, despite having a smaller (tiny) tank.
I don't know the AC input impedance of the Univox tank, but the DC resistance is close to what the DC resistance reads on the new tank.

Bread-boarded the circuit and hooked it all up and...
It sounds ok. 
Not a Fender, but sure a darn sight better than the clank noise it had before.

Etched up a circuit board for the reverb drive and got it all installed.
Left the disconnected piezo tank in place for posterity.

In hindsight I should have used a shorter 9 inch tank and mounted it away from the power supply side.
The long tank has the tank output close to the power transformer.
(Mounted as far away as possible)
There is a slight hum that increases when turning up the reverb control.
Moving the tank away from the chassis the hum goes away, so it is picking up from the power transformer.
The hum is not noticeable when playing, but I may change the tank out later for the short one.
Or maybe rig a shield between tank and transformer.

On to the tremolo circuit... I want to slow it down a bit...

Replaced C19,20,21 470nf caps with 1uf caps and the oscillator stopped working at slow speeds.
High speed still works and slowed down to a useable rate.

Replaced Q6 with a higher gain MPSA-18 and the slow speed came back.
It's slow to start at initial turn on, but works reliably once it starts.

Speed range is now more to my liking. Works great!

Side note;
Have a look at Q7, Q8 and the circuitry around them.
Seems like a lot of rigmarole just to drive a speed indicator lamp!
Node "C" from the P/S is solely for this function!

I took power from this node for the reverb drive circuit because when I tried taking power from any of the other supply nodes; it would load down those nodes too much. (Several volts)

Node "C" only dropped from ~ 14V to 12V with the reverb drive circuit added.
The power at that node does pulse a bit, but does not seem to affect the reverb. Maybe it even adds some ambiance.
Side effect; the speed indicator lamp is a bit dimmer than before.
Who watches that lamp while playing?


Input impedance looks dismal.

Rewired the #1 and #2 input jacks to Fender style with a 1 Meg and 68K resistors. (Shown on the schematic as J1a, J2a etc)
Much better.
Guitar noticeably brightened up on the thin strings.
Was gonna put a buffer on J1 and 2 but the Fender style input works pretty good.

Not sure yet what to do with the Voice channel.
Maybe an input buffer, or make an adjustable gain input with clipping since the control is already there.

Can someone please tell me what this part is?

The marking on it reads Toshiba and it measures approx 180 ohms.

I suspect it is a NTC resistor but would like confirmation.

Thanks! 

Finally got this one done. 

This thing was a basket case when I got it.
Cracked circuit board and broken copper traces.
4 transistors NFG. Q4,5,6,7 all measured open across B>E B>C
One burnt resistor (R15) , so bad I could not read the color bands.

Interesting Power amp section... Very similar to the Sears 40XL.
Because of the similarity, I used the value from the Sears amp (R17, 68R) for this amp (R15).
Seems to work ok.

This amp is waaaay louder than the Sears amp!
Even going to the same speaker.

No mods to this other than to use 2200uf filter caps for C31, C32, and the mentioned R15.
I did replace ALL other electro caps with same value, and all ceramics with mylar "greenies", with the exception of the 4 trem osc "tootsie roll" 470nf caps.
Those I left alone as they work ok, and the trem speed is fine. Maybe not quite as slow as I like, but ok.

Other things... Added 3 wire grounded AC cord, removed the "death cap" and disconnected the line reverse switch.
The original Q7 markings are unreadable except for "RCA". Installed a Motorola 2N297A in its place.

It sounds surprisingly pretty good! Loud with nice "transistor breakup" above 6 or 7 on the volume.
Could gig with it thru a decent cab.

Q5,6,7 all get very hot, so much so that you cannot touch them for long when the amp has been on at full vol for a few min.
Also R16,17 get hot too.

I rewired everything and made a harness and connectors so it's easy to remove the board to work on it.
The vintage reverb tank is fine and functional. 

Here's the schematic and layout,
and the Sears amp schem for reference.

Edit; I didn't have a 2N3711 for Q4 so I used a metal can 2N2222. works ok.

The seller didn't know the pedigree of this amp...

These are his pics from the listing.

It does have a full size Gibbs tank in it.
No ID numbers on the tank. (not that it would help ID the amp)

No speaker cab with this one.

Hard to get good pics of the front, the "black chrome" face plate makes reflections that mess with the camera.

No name anywhere on the amp.

Thanks!

Once again.... 

I have discovered an eBay gem? Ha Ha! 

When I got this I thought it would be a candidate for a "real" chipamp like a LM3886.
But after playing with it and changing some component values I think I'll keep it with the original chip amp.
It's a TA7202P and I can't find a data sheet for it, but lots of NOS on eBay if I need to replace it.
The eBay sellers say it's a 6.5W chipamp.

Is this one of the "first" chipamps?

Plenty loud thru the original 2X12 cabinet.

Looks like the original TA7202P was already replaced as the copper tracks are mangled, but whoever replaced it, they managed to get it working.

2 schematics here, the first with the "original" parts values as it came to me.
It all "looked" original except for the TA7202P.

The second schem is after I played around with it some.
Parts changes are... R3, R4, R5, R10, R17, R23, R20, R21, R25, C12, C14, C15, C16, C17,

One BIG improvement was to change R3 to 1M.
The amp got really LOUD when I did this, but the trem stopped working.

Fiddling around with the trem circuit, I got it working again.
Parts values as shown in the schematic and layout.

If you look at the thread with the National GA-920-P amp, you will see some similarities to this one,
re; the input stage and the trem circuit.

Since the National already sounds good I "copied" some of the parts values.

This thing actually sounds quite decent for an 80's SS "cheap and cheesy" amp. 

Note; I did replace ALL electro caps and this made a huge improvement, including the chip amp has a turn-on delay that was very loooong with the original caps.
Now the turn-on delay is very short. Maybe 1-2 seconds. Before it was about 6-7 seconds.

Fun amp. 

Oh, the 2X12 cab has some no-name drivers, 8 ohm each, wired in parallel for a 4 ohm cab.
Lotsa bass!

Oh ya, the original transformer was replaced at some time, the mounting holes are different.
No matter it seems to work ok.

Finally got this one done.

EDIT; removed schematic from this and other posts, see later post #19 for correct schematic. Thanks!

The schematic for the solid state version of this amp is unobtainium.

This amp may be better known as the 1422 and started life in the late 60's as a tube amp.
By the early 70's it became Solid State and has a model # 14222.

Schematic for the tube version is easy to find.

I've seen a few folks asking on other forums for the SS version schematic, so, here it is! 

Found on ebay with a seller made cab and a non original vintage speaker.

Tremolo and reverb were not working. Fixed now. Bad reverb tank and a broken trace for the trem.

Note the weird tremolo circuit, Q8 collector goes to ground.

Cheers!

Found this on ebay, price was right.  Came with the original owners manual including the schematic. 

Seller had already tested it, so when it got here I plugged it in and it fired right up.
Great! No noises, no hum sounds pretty good. Ok, so....

First thing I noticed was the "death cap" C7 so removed that, and added 3 wire safety grounded IEC socket.

I could not figure out where the circuit grounded to the chassis, so to be sure,
I added a ground wire from the circuit board direct to the chassis, right next to where I grounded the IEC socket.

Now the amp hums/buzzes like hive of angry wasps.

Fairly sure I introduced a ground loop somewhere/how.   

So gonna pull the ground I added and see, but too tired tonight to work on this anymore.

Here's another "mini stack" amp that I found on ebay.
This one has the Domino logo on the speaker cab but no name of any kind to be found on the amp head.
The seller didn't say, but I assume it came from an estate sale, as that is where many of his items come from.
I suppose the 2 pieces could be from different places, but it came with an ancient looking speaker cord and everything looks untouched/original.

No schematic so I traced the board to create one.

The amp works ok, but has excess distortion, esp on the low notes.
I replaced all electro caps and many of the ceramics with plastic film caps. Same values.

Sounding better, but still too much distortion on the low notes. Very "Fuzz box" sounding.
I don't think it was meant to sound like this.
Backing down the volume to whisper quiet, it cleans up, but still distorts if you strum hard.

Putting a 1kH 200mV sine signal at the input (or playing guitar into it) and tracing the signal with a scope, all is fine until Q3.

At the collector of Q3 the bottom half of the waveform is severely clipped/flattened out, like it's hitting the rail.
Power supply is solid, very little sag, even at high volume.
Top of the waveform seems to have miles of headroom.

Any ideas?

Thanks 

Edit; Moved some things around in the power amp section to make the schem easier to read.

This is the Sentient Machine I built with the board from Parasit Studio.

The Rate knob flashes with.... well... the rate. 

Arnie's eye lights up in effects mode.

Here's a demo... not me playing.

https://www.youtube.com/watch?v=D-L_0JkeNF0

I want to get the red LED to be just a pin point of light.
I need to mask it somehow.

I just won this amp on eBay auction.  .... for cheap.       

A couple of searches yielded very little information about this amp.
I'm just trying to get a head start as the amp was listed as having issues and I'd like to find a schematic for it.

Here's the sellers words describing the problem.

"In terms of function, this Unicord powers on and passes signal.
But, there is a short somewhere causing squealing- you can hear the short if you tap on the top of the amp.
The reverb squeals as well and the pots have moderate static.
The horn in back does not pass signal."

Possibly an easy fix but of course I'll know more once I have the amp in hand.

Hoping that some of our (ahem) senior members might remember these, or even have a dusty old schematic tucked away somewhere.

Thanks for any help! 

I have this U65G amp that has DC approx 4V on the speaker leads when the speaker is DIS-connected and .007 VDC with the speaker hooked up.
There is some low level hum with the vol at 0. Somewhat more when operating, and a bit of hiss.

The amp sounds fine otherwise, and running it at full volume with a lamp limiter it barely makes the 25W lamp filament glow.

Here's the schematic.... as far as I can tell... the DC seems to be coming from the emitter of Q2. Is this normal for this amp?

I have replaced the 330uf at the speaker output, the 33uf at Q2, and the .001 at Q9, even tho they tested ok.

I should mention that if I power the amp with ONLY the voltmeter on the speaker leads, the meter reads approx 12V at power on, and then rapidly falls to ~4V.

With the amp running and Vol on 10, speaker hooked up, I get 3.9V at the emitter of Q2.
What should I check next?

Thanks for any and all help.