Supreme (Garnet) Amp

[mtlbasslad]

Not even finished with the Ampeg but now I have this tiny Garnet clone with the 'Supreme' badge on it.
Looked through all the Garnet schematics but could not find a match. This has no power trans (just a 150 ohm 10 watt resistor going to the rec tube). 35W4 rec tube, 50C5 power tube, & 12AX7 preamp.
Pretty loud 60/120 hz hum. Changed all the tubes which were ancient. There is a Nichicon can cap (which I doubt is original, it has a 99 cent price tag on it) Nichicon # 41-45271-1 - 3 caps, 750uF @ 175V, & 2X 100uF @ 250V.
Are these original values? What would be logical values for this little amp? Anyone have a schematic?
Hey g1, it's made in Winnipeg!

[The Dude]

Those cap values look high for the age of this amp. I don't have a schematic, but what you describe is a widow maker. You will need to install an isolation transformer to make it safe. It's a 3 tube amp, so ought to be pretty simple. If you can't find a schematic, just draw up your own.

[mtlbasslad]

Those cap values look high for the age of this amp. I don't have a schematic, but what you describe is a widow maker. You will need to install an isolation transformer to make it safe. It's a 3 tube amp, so ought to be pretty simple. If you can't find a schematic, just draw up your own.

Yes, first thing I noticed - no PT. As for drawing my own schematic, you are confusing me with someone who knows what they are doing LOL

[glebert]

Seems like it might have some similarities to this amp. I think both would be guitar variations on the All American 5 (AA5) tube radio circuit. Adding an isolation transformer and adding some shielding around the input on mine helped the hum quite a bit.

[35L6]

3 watts sounds a little optimistic . See where it says AC 100 V ? Secondary of the isolation transformer ( I like N-68X ) goes there . Disconnect cap and resistor to ground . Be sure mains safety ground is connected to chassis . Input tube heater at the earthy end of the heater string . Other values can be gotten from data sheets . If you can't get rid of the hum you can add another filter before the power tube supply but it will reduce power . In the end there are only so many ways to build a 3 tube amp .

[mtlbasslad]

Seems like it might have some similarities to this amp. I think both would be guitar variations on the All American 5 (AA5) tube radio circuit. Adding an isolation transformer and adding some shielding around the input on mine helped the hum quite a bit.

glebert I see only 2 40uF 150WV caps in there - like The Dude said 750uF seems a bit steep...?

[g1]

There is a Nichicon can cap (which I doubt is original, it has a 99 cent price tag on it) Nichicon # 41-45271-1 - 3 caps, 750uF @ 175V, & 2X 100uF @ 250V.
Are these original values? What would be logical values for this little amp? Anyone have a schematic?
Hey g1, it's made in Winnipeg!

This schematic should pretty much be a match. Lark was the Pepco version of it, Garnet and Pepco both did the stencils and used some of the same schematics.
See note about cap unit.

[mtlbasslad]

Thanks g1 - this looks like what I have on the bench. I see no voltages over 150 so I'll look for a suitable can cap, 20-30-50 uF or better.

[mtlbasslad]

3 watts sounds a little optimistic . See where it says AC 100 V ? Secondary of the isolation transformer ( I like N-68X ) goes there . Disconnect cap and resistor to ground . Be sure mains safety ground is connected to chassis . Input tube heater at the earthy end of the heater string . Other values can be gotten from data sheets . If you can't get rid of the hum you can add another filter before the power tube supply but it will reduce power . In the end there are only so many ways to build a 3 tube amp .

I can only find N-48X or N-51X on DigiKey - 15VA or 35VA - which one is appropriate?

[Enzo]

The amp is tiny, what is the mains fuse rating? On the other hand, the 35 watt one - is it that much larger? Is it that much more expensive? Never hurts to have more than you need.

[g1]

I'll look for a suitable can cap, 20-30-50 uF or better.

With rectifier tubes, there is a max. limit of the capacitance it can be directly connected to. So you would not want to exceed the 50uF at rectifier pin 7.
Assuming that the 750uF was connected at pin7, the rectifier tube may be damaged.

[g1]

I can only find N-48X or N-51X on DigiKey - 15VA or 35VA - which one is appropriate?

Something is wrong with their search function. I searched for N-68 in the search box and it pointed me to N-68X-B which is out of stock. But using the selector function, it finds the N-68X with 55 in stock.
https://www.digikey.ca/en/products/d.../N-68X/1887210

[mtlbasslad]

The amp is tiny, what is the mains fuse rating? On the other hand, the 35 watt one - is it that much larger? Is it that much more expensive? Never hurts to have more than you need.

Don't know the fuse rating - 2A in there now. But you are right, bigger one is only $2 more..

[mtlbasslad]

With rectifier tubes, there is a max. limit of the capacitance it can be directly connected to. So you would not want to exceed the 50uF at rectifier pin 7.
Assuming that the 750uF was connected at pin7, the rectifier tube may be damaged.

I put in a new rec tube & only ran it long enough to hear the hum. Got crazy readings on the can cap, must replace

[mtlbasslad]

Something is wrong with their search function. I searched for N-68 in the search box and it pointed me to N-68X-B which is out of stock. But using the selector function, it finds the N-68X with 55 in stock.
https://www.digikey.ca/en/products/d.../N-68X/1887210

DigiKey website drives me crazy - neverless I still don't know which of the 3 iso trans I need. All presuming 'customer' will pay... Sheesh