#1
Good evening,

I have taken an interest to the THD BiValve 30, with all of its wonderful features, as a replacement to my oversized Lambeth JL-100. As some of you long-time UG contributors know, THD is no longer in business, and Andy Marshall doesn't exactly enjoy the best of reputations 'round these parts. What's more, they're not exactly easy to find at the moment.

Is there a suitable substitute? Here are the features I really like:

Built-in attenuator
The ability to use any preamp or power amp tube, in any combination
Self-biasing
Bulletproof construction

Alternatively, are there any mods that I can perform on my JL-100, pics to follow, that will give me the first three features (the amp already enjoys impeccable build quality)?

Thank you.
Last edited by andvari7 at Nov 9, 2013,
#2
didn't know they were out of business. but i have a bivalve, love it.
Quote by andvari7
Is there a suitable substitute? Here are the features I really like:


no. i basically bought the bivalve cuz it was the only true class A amp i could find that had the features it did

Quote by andvari7
Built-in attenuator


i actually don't like the built in attenuator. if i cut any good amount of volume using it then it tends to eat up the upper harmonics too much.

imo, it sounds much better using it like a non-master volume amp.

Quote by andvari7
The ability to use any preamp or power amp tube, in any combination


just about any tube amp can use a variety of preamp tubes (12AT7, 12AY7, 12AX7, etc). but using different power tubes is a different story. some amps can use a couple of varieties of power tubes (usually either EL34 or 6L6GC's, but these amps can also generally run KT77's as well). and you generally can't use them in any combination, only as sets

i haven't found another amp that can run mix-and-match power tubes like the bivalve. i think one of the reasons it can do this is because it is class A (so each tube is cathode biased)

Quote by andvari7
Self-biasing


once again, this is because it is class A. i don't believe cathode biased amps need biasing like a fixed biased (or class A/B) amp does.

Quote by andvari7
Bulletproof construction


i've had mine in the shop once. blew a grid resistor i think. still, i would agree with this statement, mine seems like a pretty solid amp.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
Last edited by gumbilicious at Nov 9, 2013,
#3
Class A amps don't have to cathode biased and not all cathode biased amps are class A gumbi.


No attenuator but have you thought of a Randall Rm or RT? You can run pretty much any octal tubes and even odd combinations in the power amp - and they are really easy to bias. You can do it right on the back of the amp, ie no opening it up to bias it.
Modular preamps on the RM but you can stick other tubes in the modules - or mod modules. V1 is common, it behaves like a buffer for the modules. You could stick other tubes in there too. There are two other 9 pin tubes too - FX loop and phase inverter.
Just seems to me that it may be right up you alley, liking to tinker like myself.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Nov 9, 2013,
#4
Quote by Cathbard
Class A amps don't have to cathode biased and not all cathode biased amps are class A gumbi.


i should have made more of a disclaimer stating that i am not an expert on amplifier circuitry, and i didn't mean to insinuate that 'all class A amps are cathode biased...' (i would have no idea if that is true or not, evidently not). it has been a while, but i believe i found information at one time stating the bivalve was cathode biased. i always attributed it's independence on power tube usage to that feature.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
-ae
Last edited by gumbilicious at Nov 9, 2013,
#5
Yeah it is pretty much. But it's the biasing method, not its class. It's single ended cathode biased iirc.
Means your bias will be out a bit for some tubes. That whole trying to pick a mid point thing. I prefer the way Randall does it; external probe points and adjusters. Craig does that on the Brigand too doesn't he? Much better idea. Takes no time to do it and you know it's right. Not just safe, but right.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Nov 10, 2013,