• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My debut into the vacuum world: Yarland FV34B

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Hi all, this is even my debut here in this forum.

Just today I got from a friend a Yarland FV34B, doing my debut into the vacuum world (soo amazing, I will never go back to transistors), with tubes already changed:

x2 preamp 12AX7 Electro Harmonix
x4 amp 6L6Y RCA

Btw I wish to change the amp tubes with a set of KT88 that I prefer far far more than the 6l6y.

It's possible to do that if I keep the 2 preamp?

There's no way to modify the bias so I've to buy a matched set of KT88 right?

And last but not least :p any kind of modification suggested that heavly improve the FV34B?

I'm sorry if I'm shoting all those questions already but I feel like a kid in a new magic world :D
Stick to the 6L6s. KT88s will put too much pressure on the power trafo. Also, the O/P trafo primary impedance for KT88s is approx. 1/2 that of 6L6s.

From what I see on the WWW, the amp works with EL34s and KT66s (roughly = 6L6GC).

The EH 12AX7 is (IMO) no better than mediocre in HIFI service. Installing the Sovtek 12AX7LPS in those "holes" is an inexpensive way to improve "tone".

Without a schematic, it's difficult to make rational recommendations about tweaks. As the owner, is a schematic available in the documentation packet? If so, scan and post it.
I dont have the schematic, actually I'm searching into the web in case someone has it.

This is the amp btw: audiocostruzioni.com

What I can report is that the old owner and our official national distributor told me that this amp is fully compatible with El34, KT66, KT77, 6l6, 5881, KT88.

Maybe someone else here know deeply this amp and can share more info/suggestions.

I managed to communicate with Yarland by e mail, but the reply was a bit broken English, assuring me I should take my faulty FV34b to a skilled technician, despite me reassuring them that I was skilled, just completely out of touch, not wanting to spend the time tracing the circuit, and in need of a diagram - I am an ex TV engineer, qualified in all sorts of solid state Hi - Fi like B & O, Sonab, Nad,etc.
Low on valve experience.
I did manage to re - bias my Marshall JCM 900 to go back to its original valve line up - involved changing a few resistors - no probs - works beautifully.
Problem - Yarland died age 4 years old.
Power supply MR67 diode blown. Replaced and blew again - replaced, checked all that I could going by the cct diagram Yarland had sent me - which was hopelessly wrong - even just going by the used components.
I only found a transformer tapping wire looking suspiciously poorly insulated - so I corrected that and tried again - Eureka - the sound of music - for 3or 4 minutes, then an annoying hum and no music. Darn!
I have a fault I cannot see, and lack of time - it is very close to defeating me. Attached circuit diagram as supplied - mine has no chokes, and 2 200 ohm resistors.


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I have just had an epiphany - you know one of those that make you feel a fool - I haven't tried the amp with no valves since it first blew up - that's what these diodes feed - the HT to the valves - can't wait to attack it now - might be simply a short in a valve - maybe with it being upside down, and electrode has sagged back to the way it should be, until it warmed up again - then bang..........
More good news - I replaced MR67 diode and took all valves out - tried pre amp first - all 3 ok - O/p stage left - OK after 2- 3 minutes (all with original 3A fuse, so I hoped this would blow before a component - last 2 o/p el34's - one had a peculiar mark round the top, and I had noticed that this same valve was 6-8mm taller than the others - so it didn't feel like a matched pair for a start - has the retailer been a bit naughty?? fortunately, I had changed My JCM900 4100 El34's for quad matched 5881's (after changing the resistor values to re bias) so I had a spare pair - put them in and eureka - result.
This was just as well, for I had ordered a 'Little Bear' valve phono pre - amp, and it had arrived - I put it in line to replace the solid state phono, and it all sounds just beautiful - value for money!
Remember that if you change valves, especially the type (no.), they will need re biasing anyway, and if you change the type, they may run very hot to damage, or too cool to sound correct. I have a good article on biasing if anyone wants it.
Incidentally, I have just realized, I am probably talking to myself on this one, since the original article was 5 years ago - I must be in a time warp..........
same amplifier but


i've got a yarland fv-34b too, but input valve is 6F2 (6U8, ecf82) and i have no more sound ! i replaced all tubes, EL34 and 6U8, bias is ajust to 0.30v as indicated, no cut off on output transformers, i can't find the schematic.
have you got any idea ?
regards !
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