Sunn Solarus lots of hum

[kupervaser]

Will this head work without the reverb tank or should I put that in first?

[Soundmasterg]

It will work fine without the reverb tank installed. You just won't get working reverb without the tank.

Greg

[kupervaser]

I looked on the inside of the amp and noticed that two of the 1000uf capasitors (the yellow once) had broken leads.



That could be the source of the problem. Still haven't got my step down transformer to test it. I'll replace the capacitors and measure some voltages.

[kupervaser]

Soldered the caps yesterday and put in the EL34 tubes. The amplifier started working instantly.
Sounds good, only there is some hum, probably 50hz from the wall outlet hum. Or is there a chance the step down transformer can deliver such hum?

Also, what are the big capasitors on the left for? I can;t seem to find them on the schematic:

[Oli]

Or is there a chance the step down transformer can deliver such hum?

Hi,
I had no trouble with my Step down concerter (so far.... ). Do you use a "grounded" cable? Otherwise you can use the polarity switch (you should change it to a "grounded" cable as soon as possible!!!!).
I would also check the 600V caps, my amps produces "neary" no hum with new caps. They are not that expensice.

Greetings

Oli

[kupervaser]

I do not see those big capasitors on the left on the schematic. Do you have any idea what they are for?

[Ryan Phelps]

Kupervaser,
The silver Mallory capacitor is the original filter cap for the first pre-amp tube V1 (12AX7A / ECC83) and should be connected to pins 1 and 6. On some Sunn amps, one of the stages of the 4-section can capacitor was not used (or was used in parallel with another section) and a discrete capacitor was used locally next to the tube it served (in this case V1). It appears that the silver Mallory was left in place and bridged with a new gold-colored capacitor.

Ryan

[Soundmasterg]

Kupervaser,
The silver Mallory capacitor is the original filter cap for the first pre-amp tube V1 (12AX7A / ECC83) and should be connected to pins 1 and 6. On some Sunn amps, one of the stages of the 4-section can capacitor was not used (or was used in parallel with another section) and a discrete capacitor was used locally next to the tube it served (in this case V1). It appears that the silver Mallory was left in place and bridged with a new gold-colored capacitor.

Ryan

And both of those are bad too most likely. On the schematic it would be the electrolytic for the first stage...either the supply cap, or the cathode bypass cap. What is the value of that gold cap in the pic?

Greg

[kupervaser]

The silver one sais 20uF and the golden one sais 50-60uF.

[Ryan Phelps]

Both of those caps are physically too large to be cathode caps. And by their values, it's apparent that they are power supply filter caps. The "+" side should go to pins 1 and 6 of V1 and the "-" side goes to ground. The gold cap is too large (in capacitance) for filtering at the 1st stage. And Soundmasterg is right, they are both too old. They should both be removed and replaced with a single 20uf x 450V electrolytic capacitor.

[kupervaser]

Do I need to put a bigger output transformer if I want to use KT88 tubes in this amplifier?

[loudthud]

Do I need to put a bigger output transformer if I want to use KT88 tubes in this amplifier?

No, but don't expect any increase in power. Your output power may in fact be slightly less with KT88s.

[kupervaser]

Thank you, and if I would like to have more power, what kind of a transformer should I be looking for?

[Isaac]

I'd say that, if you're looking for significantly more power, you should be looking for another amplifier.

A pair of 6550's can put out around 80 watts. A pair of KT88's can put out around 100 watts. That's a difference of only about 1dB. Hardly worth it. Even compared to the lower 60 watt output of the tube-rectified Sunn amps, it's still only 2.2dB.

If the Solarus is giving you the tone you want, and no other amp will do, then either mic the speaker, arrange for a line out, or get another amp and speaker.