Supreme (Garnet) Amp

[glebert]

Does the hum go up and down with the volume? Also, is it 60 or 120 cycle hum? If necessary download an audio spectrum app for your phone.

[mtlbasslad]

I must say, that really doesn't help us help you. What does "crazy readings" mean? Be specific.

My apologies Enzo (& everyone else) for that foolish post, must not post anything after happy hour.
So to do it right I removed the cap can & got these readings - 750uF section reads 865uF, the 2 100uF sections read 112 uF.
As has been pointed out, that is too much for this little amp & rough on the rec tube... but if the can cap wasn't dead, where is the hum coming from?
I will take the good advice & source radial caps & terminal strips... I wonder if I can find those at DigiKey. I'm pretty sure the nearest parts place would have them, but it's 50km away & the price of gas makes it better to order online.

@g1 can you email me the schematic please? I could not print it out from your post, sigh.

[glebert]

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

When I put an iso into my Melody amp I found there really wasn't any place to mount it up on the chassis, and would have actually made the amp quite top-heavy since it is such a minimal amp. I ended up mounting the iso transformer down on the bottom of the cabinet and then used a set of 5 pin molex connectors to take make a quick disconnect so that it wasn't like wrestling a squid when I tried to work on it.

[The Dude]

FYI: You don't need a 3 cap can. You could save money by using separate caps and even more money if you use radials. I would use radial caps and terminal strips. There's usually plenty of room in those older amps.

[g1]

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

Use the 68, it has the highest VA rating, so most capable. The $ difference is negligible so may as well use the best one.

[Enzo]

Got crazy readings on the can cap, must replace

I must say, that really doesn't help us help you. What does "crazy readings" mean? Be specific.

[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

[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]

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..

[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

[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.

[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.

[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?

[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.

[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.