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Different GZ34 brand yields more headroom...BadCat Black Cat 30

sixstring531

Silver Supporting Member
Messages
3,199
I was bored and decided to break out the old Heathkit tube tester and make some notes with the spare used old stock 12ax7s I have laying for my Black Cat. All tested around 93-95%, though I don't know how accurate the old thing really is. That said, the amp always sounds awesome - but as usual I'm always tinkering - and I thought I would move some tubes around see what differences I could hear.

Pre move:
12ax7
v1 - old stock GE labelled Mullard (longer plate, not longest I've seen, two lines on top of outside of tube)
v2 - new production Sovtek 12ax7
EF86
V1 some gold pinned thing - my favorite new production EF86
V2 new production Ruby 12ax7
PI
Sovtek 12ax7LPS (the only thing I run in the PI for Matchless/BadCat)
Power tubes
4xEL84 JJ (changed yearly)
Rectifier
Ruby GZ34 (chinese I believe)

Change:
12ax7
v1 - old stock Sylvania - long dark plate
v2 - old stock GE lablelled Mullard (used to be V1)
EF86
V1 some gold pinned thing - my favorite new production EF86
V2 old stock long black plate (not sure of the brand)
PI
Sovtek 12ax7LPS (the only thing I run in the PI for Matchless/BadCat)
Power tubes
4xEL84 JJ (changed yearly)
Rectifier
New production Genelax Gold Lion GZ34 (looks like Sovtek)

Several things to note: It still sounds amazing, but I have quite a but more headroom than I did. Where it used to start breaking up at around 10 on the 12ax7 dial it now stays pretty solid until about noon. All volumes are comparable, but it just breaks up a little later. (and sounds like $1mm!)

Right now I am leaning to the rectifier being the culprit. As I understand it the chinese (Ruby) is a truer 5AR4, which doesn't provide as much voltage to the power tubes - causing them to break up earlier. The Sovtek/Gold Lion I switched to is not a proper 5AR4 and provides more than enough voltage, which makes them more efficient.

I don't have the set up at the house to swap and then test, but the easiest thing to do would be to swap the rec and try again, to rule out the Sylvania/Mullard in v1. I'll give it a whirl next time I have everything out and available. I'd love to do quick swap/tone tests on v1, but the transformers are so big and space is so tight I would have remove the chassis again.

I just thought I would share!
 

hardys

Member
Messages
1,738
The only way to really test that out is to do it one tube at a time, other than the power tubes with 4 at a time.
 

RussB

low rent hobbyist
Messages
11,158
But you changed many tubes. How do identify where the added headroom came from?
 

Blue Strat

Member
Messages
30,190
But you changed many tubes. How do identify where the added headroom came from?
Yep, all you can do is guess with that many changes. Why guess when you can swap just the rectifier and find out for sure?

It's a good theory though.
 

sixstring531

Silver Supporting Member
Messages
3,199
I was waiting for Blue Strat to pipe up! I know it's flawed, but it made sense in my head. I'm thinking I've used this V1/V2 combination before (I've had these tubes a while) and don't remember the headroom coming until the rec change. That said, I'll definitely do the rectifier swap next chance I get. It's the easiest and most accessible on the Black Cat.
 




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