Soldano Avenger help needed

[Drewline]

Hi,

I originally posted this in schematic needed, have received no replies & am reposting my question here in hopes of someone knowing what is causing this problem. Thanks in advance.

Soldano Avenger Schematic Needed


I'm looking for a Soldano Avenger schematic. I've got one in for repair that has a hum which increases when the Master is turned up & when the preamp is turned up. The preamp noise sounds like high gain, the master noise is more of a hum. The noise is coming from around V3 which is where the circuit differs from the SLO100

Thanks,

[Jazz P Bass]

Not having the schematic, I must ask, 'What have you checked so far?'

Plate voltages (Vdc & Vac), cathode voltages, grid voltages.

That's a start.

[Chuck H]

Also, do we know any history on this problem? When did it start? Has anyone else worked on the amp? Any history?

If a schematic isn't offered by the MFG and one can't be found on line we'll be diagnosing an unknown circuit. Ergo the Q.

[Drewline]

I've checked tubes, checked components for shorts & opens, subbed the filter caps near V1, V2 & V3. As near as I can tell the amp hasn't been serviced Nothing obvious stands out. It came in from a dealer who specializes in used gear. The only schematic I've found is for the SLO 100. If I'm following this correctly, the Avenger uses one less preamp tube.which is a combination of V3b & V4a on the SLO circuit. There is no effects loop which is between V3a & V4b. The tube, V3, looks to be a cathode follower. My voltage measurements are: DC pin1 271, pin2 0, pin3 2.22, pin6 398, pin7 272, pin 8274 AC pin1 .19, pin2 0, pin3 0, pin7 .19, pin8 .18, pin9 3.3. Filaments read 6.5Vac.
If I did this right, I've attached the SLO100 schematic.

Thanks,

[Drewline]

Hi,
I was wondering if anyone had any ideas on this problem. I've isolated the problem I think to V3 the cathode follower preamp tube which feeds the tone stack. Nothing is defective that I can find. Is there any way a pot or the power supply filter caps could cause something like this?

[guitician]

Have you substituted the output tubes? There was a post where they were having a similar issue and couldn't find the source of the trouble and it turned out to be a slightly shorted tube that tested good.

[silverfox]

I took a quick look around. You might have to write one up. Perhaps a stage at a time or you could check out the site below and review all the schematics there and compare. Use as a road map. I listened to one on Youtube and it sounds very Marshall 800 ish. (At the moment the first part of the 800 escapes my mind. (Now the amp is cranked on Youtube and I just remembered JCM 800)


Free Soldano Diagrams, Schematics, Service Manuals :: Schematics Unlimited

As I'm listening to the Demo on the Tube the amp there is also humin. Perhaps that is the way it was made and you could try to mod it??

Pull all the tubes and use the headphone trick to look for hum. I'm a novice so keep that in mind.


https://www.youtube.com/watch?v=qrHuQvSnMKg

Silverfox.

[Mick Bailey]

If you think it's V3, short the grid to ground. If the problem stays, it's likely to be V3. If not, one of the stages before. Your MV affects the hum, so the output stage is likely to be OK if the hum goes away with the MV turned down.

[Drewline]

Hi all,
I wanted to say thanks for the advice & help with this. I finally got back to the Avenger today & resolved the issues. It turns out there were 2 problems going on at once. The first problem was the input jacks were internally corroded giving a low resistance on my DVM. The low input which bypasses V1 goes to the gain pot. With the switches giving readings of 2-3 ohms instead of 0 ohms, I got noise like an open input. Changing both jacks resolved that problem. The second problem was the amp's as received preamp tubes, Mullard reissues. I had previously changed all the tubes which didn't solve the problem. I spoke with Mike Soldano about the amp & he told me to check the preamp tubes, that the amp was very sensitive to what tubes were in it. Soldano has switched to & recommends JJ ECC83 which are low noise in these amps. I switched to JJ's & moved them around until I found the right arrangement of tubes. With JJ's in V2, V3, V4, Gain & Master dimed, it was acceptably quiet. V3 seems to be the most sensitive to the particular tube installed. With the low gain input shorted I tested the Mullards in V1. All 4 of them had a very high noise floor, 2 of them causing a hum in addition.
Another piece of info I learned from Mike is that there are 2 versions of this amp. Early production, like mine, use AC filaments. Later production was switched to DC filaments.
I have a schematic partially drawn out on the actual circuit of this amp that I will clean up & post here for anyone in need of it.

[nsubulysses]

Drewline I am in need if you have any Avenger schematic to offer

[Drewline]

See post # 4. Also see post #9. The Avenger is a simplified version of the SLO. Unfortunately I've lost track of the Avenger schematic I started to draw out. I'll look in my file at work next Monday & see if it is there & if so I'll scan it & post it here.

[nsubulysses]

Ok, I have the SLO schematic already. if the Avenger comes up please post but if not I will just work off the SLO schematic thanks