Steel String Singer #005 build

[captaincoconut]

Thanks, but now a question for all you real tube amp professionals in this forum: I was able to lower the bias pot range by replacing the 56k resistor feeding the balance pot with a 33k resistor. I'm now able to bias the tubes from around 30mA up to well above 60mA. Sweet!

I then spent the afternoon test driving the amp for the first time. In order to get some juice out of the power amp I connected the amp to my Fryette Power Station PS-2A. Unfortunately, even with the master volume right in the middle I get some nasty distortion happening. Not the good power amp overdrive one would expect - it sounds more like when you overdrive the input of your USB interface, not pleasant at all. It's not much and only if you really strum harder, but even with my low output Stratocaster it happens quite fast.

I initally thought that this was occuring somewhere in the preamp, so I pulled the power tubes and went from the preamp output into the line in of the Fryette, basically using the Fryette as the power amp. The result: beautiful angelic clean sounds. Even with the preamp volume all the way up - no distortion. When stacked with the FET booster I get some slight - really cool sounding - overdrive happening.

Hm...so this must happen somewhere in the power amp stage.
- The phase inverter isn't balanced yet, but the parts in there were closely matched and I'm even using a balanced phase inverter tube, so it shouldn't be too far off. Would this contribute to the problem? I played around with the trimmer and that didn't change anything in that regard.
- I played around with the bias between 40mA and ~55mA. No change.
- My build has 22nF coupling caps after the phase inverter. The original layout had 47nF. Should I try the original value?
- GNFB resistor is 100k from the 8 ohm winding.

Can't think of another source for the problem right now...any help appreciated!

[martin manning]

Great to hear that the preamp is sounding good. I'm guessing that you have a parasitic oscillation in the PI section. What are the voltages through the PI and power amp now?

[captaincoconut]

Here are the voltages measured about 20 minutes ago (blue are Beasley's build, red are mine):



Note: I have the FX loop sitting between master and the PI input cap. The presence circuit has the position of the cap and potentiometer reversed.

[martin manning]

That all looks good. Try placing another cap across the 68p "fizz" cap, maybe 100-150p, and see if that changes anything. If it does, that would pinpoint the problem.

[captaincoconut]

Only bad news today, folks:
1. I replaced the 68pF cap with a 330pF cap (that's all I had on hand today) and the fizz did not get away. It didn't even change the slightest.
2. On top of that, my Fryette Power Station crapped out today. I just bought it used about two weeks ago, the unit itself was built in February 2025. It started with what I would have diagnosed as tube noise, but now I have a permanent hum on the Fryette's output. Tried two new 6L6 pairs but to no avail.
3. I put the SSS chassis in the headshell today and played it at room volume. Sounds really really cool, no fizz, no nothing. I'm wondering if the fizz was caused by the beginning to fail Fryette? Hard to tell...

Sigh...this is frustrating. I will have someone more experienced than me take a look at the Fryette (seller refuses to do anything...) and put the amp back on the project bench for a few days. It's summer, better to spend some time outside anyway.

[martin manning]

1. I replaced the 68pF cap with a 330pF cap (that's all I had on hand today) and the fizz did not get away. It didn't even change the slightest.

Now you know what it isn't ;^)

[captaincoconut]

1. I replaced the 68pF cap with a 330pF cap (that's all I had on hand today) and the fizz did not get away. It didn't even change the slightest.

Now you know what it isn't ;^)

The problem is that I will never get to crank the amp to volume levels where those oscillations start to happen. I could just call it a day and say, hey, it sounds great (it really does), but it bugs me knowing that there is still something waiting to be fixed.

[Matt J]

Only bad news today, folks:
1. I replaced the 68pF cap with a 330pF cap (that's all I had on hand today) and the fizz did not get away. It didn't even change the slightest.
2. On top of that, my Fryette Power Station crapped out today. I just bought it used about two weeks ago, the unit itself was built in February 2025. It started with what I would have diagnosed as tube noise, but now I have a permanent hum on the Fryette's output. Tried two new 6L6 pairs but to no avail.
3. I put the SSS chassis in the headshell today and played it at room volume. Sounds really really cool, no fizz, no nothing. I'm wondering if the fizz was caused by the beginning to fail Fryette? Hard to tell...

Sigh...this is frustrating. I will have someone more experienced than me take a look at the Fryette (seller refuses to do anything...) and put the amp back on the project bench for a few days. It's summer, better to spend some time outside anyway.

Did you buy it new with any type of warranty? Really odd for one to crap out like that right after you just got it!
Matt J.

[captaincoconut]

Did you buy it new with any type of warranty? Really odd for one to crap out like that right after you just got it!
Matt J.

I bought it used from our local equivalent to Craig's List, the seller bought it in March this year. In the EU manufacturers are obliged to give a 2 year warranty on any of their products. Many retailers like Thomann add another year, so most of the time you get a warranty of 3 years. That's worth something, huh? Unfortunately, this plays no role when buying used goods.

[Smitty]

If it were me I'd circle back with the person you bought it from and ask if they'd be willing to help you with the warranty. If they haven't registered it with the manufacturer you may be able to simply register it and submit it for repair.

[captaincoconut]

If it were me I'd circle back with the person you bought it from and ask if they'd be willing to help you with the warranty. If they haven't registered it with the manufacturer you may be able to simply register it and submit it for repair.

Thanks, but the seller already made clear it's none of his business at this point.

[captaincoconut]

[GAStan]

Nice looking amp!

Great job on the VOX grillcloth, I know from experience its definitely a challenge to get it as even and straight as you did.

[captaincoconut]

Nice looking amp!

Great job on the VOX grillcloth, I know from experience its definitely a challenge to get it as even and straight as you did.

Thank you! The headshell is definitely something I don't want to make again on my own.

[captaincoconut]

I had the amp running for a few hours this weekend and I'm really happy with the outcome now. It fills the role of the Eric Johnson dirty rhythm amp wonderfully. I threw a BC183 Fuzz Face, TS808, MXR Digital Time Delay and MXR Flanger/Doubler (the old rack units Eric has been using since forever) in front and the amp takes them like no other.