Parson 1975HW on the bench

[HomespunEffects]

My friend’s Parson head stopped working and it let out the magic smoke. One of the 10k dropping resistors burned out. I replaced it and the amp works. It had a microphonic tube in V1 so I replaced it. It had crappy no name EL34s so I replaced them with EHX. Sounds really nice, maybe a little on the bright side but it cranks.

I checked the bias and it’s running rather cold. 9.2 and 11.2 watts on the power tubes. I’d like it to be 15 - 17.5 but there is no bias pot. I’m not sure I want to add one or just give it back as is in the condition he’s used to.

What’s your opinion on leaving it alone in its cold biased state since it sounds great?

37% and 45% dissipation seems really off. I think I’m going to have to do something about it.

 

[TSJMajesty]

I don't know much about amp tech, but I know a few things about customer service, and discussing things they should consider doing, using my own expertise to explain why I think they need a particular thing done.

I'd simply talk to the owner, give them your reasons, and let them make the choice.

You did say it sounded great though, as is. Which makes me wonder why you "...think I’m going to have to do something about it."

 

[HomespunEffects]

My friend gave me the choice to leave it or change it. Just mulling it over and was seeing if typing it out would help the decision.

I’ve never run an amp below 60% dissipation.

 

[HomespunEffects]

I’m going to add a bias potentiometer so that there’s no issue in the future with changing power tubes.

 

[HomespunEffects]

I got it up to 16 and 17.2 watts. I was going to mess with the imbalance but it’s not causing any issues. This one is complete.

 

[FuzzyAce]

I don't know much about amp tech, but I know a few things about customer service, and discussing things they should consider doing, using my own expertise to explain why I think they need a particular thing done.

I'd simply talk to the owner, give them your reasons, and let them make the choice.

You did say it sounded great though, as is. Which makes me wonder why you "...think I’m going to have to do something about it."

It's easy enough to make it adjustable and it gives the ability to dial in the range better with different sets of tubes.

 

[FuzzyAce]

I got it up to 16 and 17.2 watts. I was going to mess with the imbalance but it’s not causing any issues. This one is complete.

Is this a newer amp, never heard of them?

 

[HomespunEffects]

Is this a newer amp, never heard of them?

No, it’s a Chinese knockoff of a Marshall JMP. They are actually not terrible. Handwired, eyelet board. Just cheap components and really cheap transformers.