Hello,
I recently purchased this amplifier and have questions about adjusting the bias and what mods would be worthwhile for an older amp like this? Things I’m thinking about include:
- replacing the power supply filter caps with newer and possibly bigger ones. I know they lose capacitance as they wear out.
- getting a new matched tube set, maybe Genelex KT88, 6922 tubes. In that case I’d need to adjust the bias ... need to learn that.
- maybe replacing the MIT small signal coupling caps with something different. Not sure what?
Any thoughts on good hot rod mods? It has some audible noise when listening with ear close to my 94 dB sensitive speakers, but not from a distance.
I’m an electrical engineer with experience building my own audio gear as well as a power amp I designed, but know very little about tubes ... next to nothing!
VT130 schematic:
Download Error - Schematics Unlimited
I recently purchased this amplifier and have questions about adjusting the bias and what mods would be worthwhile for an older amp like this? Things I’m thinking about include:
- replacing the power supply filter caps with newer and possibly bigger ones. I know they lose capacitance as they wear out.
- getting a new matched tube set, maybe Genelex KT88, 6922 tubes. In that case I’d need to adjust the bias ... need to learn that.
- maybe replacing the MIT small signal coupling caps with something different. Not sure what?
Any thoughts on good hot rod mods? It has some audible noise when listening with ear close to my 94 dB sensitive speakers, but not from a distance.
I’m an electrical engineer with experience building my own audio gear as well as a power amp I designed, but know very little about tubes ... next to nothing!
VT130 schematic:
Download Error - Schematics Unlimited
You may replace powersupply can caps, to ones with same capacity and voltage.
As for the rest, learn to set bias with the current tube set and do nothing more !
After you have "learned the sound" get a replacement 6550 tubeset, no need to replace
anything else.
As for the rest, learn to set bias with the current tube set and do nothing more !
After you have "learned the sound" get a replacement 6550 tubeset, no need to replace
anything else.
Follow the servicing instructions from the service manual for adjustment procedures.
Electrolytics don't wear out they dry up when abused or left unused for a long period of time.
Looking at the service manual, the amplifier uses a lot of non preferred values and to increase the values of the capacitors or play around with what I am led to believe is a premium brand and design, is not a good or reliable thing to do.
Study the service information first.
AUDIO-RESEARCH VT130 TUBE AMPLIFIER SM Service Manual download, schematics, eeprom, repair info for electronics experts
Electrolytics don't wear out they dry up when abused or left unused for a long period of time.
Looking at the service manual, the amplifier uses a lot of non preferred values and to increase the values of the capacitors or play around with what I am led to believe is a premium brand and design, is not a good or reliable thing to do.
Study the service information first.
AUDIO-RESEARCH VT130 TUBE AMPLIFIER SM Service Manual download, schematics, eeprom, repair info for electronics experts
Older amp?
It was manufactured only about 20 years ago.
Those amps are built with high quality already in mind, and a complex system to regulate bias voltages.
The official service manual warns of the exteme internal voltages, and even provides a special insulated tool if any adjustments are needed.
As a tech, and already inspecting my own copy of the service manual, I really don't recommend messing with or changing something already is highly designed already.
The diamond is already cut and polished professionally.
It was manufactured only about 20 years ago.
Those amps are built with high quality already in mind, and a complex system to regulate bias voltages.
The official service manual warns of the exteme internal voltages, and even provides a special insulated tool if any adjustments are needed.
As a tech, and already inspecting my own copy of the service manual, I really don't recommend messing with or changing something already is highly designed already.
The diamond is already cut and polished professionally.
Jon, Thanks for that link to service manual.
That’s why I ask here before diving in ... I’ve read others with this amp prefer the KT88 over the 6550 , but I also know that AR stands by the 6550. Just a matter of preference or performance perhaps? I have a distortion analyzer.
Yes, a premium brand, but what can I say, I like to try stuff! I won’t be changing anything like bias points, or parts values or such ... likely blow something up. If it were solid state I’d be more adventurous, but I don’t know Tubes.
That’s why I ask here before diving in ... I’ve read others with this amp prefer the KT88 over the 6550 , but I also know that AR stands by the 6550. Just a matter of preference or performance perhaps? I have a distortion analyzer.
Yes, a premium brand, but what can I say, I like to try stuff! I won’t be changing anything like bias points, or parts values or such ... likely blow something up. If it were solid state I’d be more adventurous, but I don’t know Tubes.
The trouble with "others" and the internet "blogs" they frequent is....
They're not reliable sources.
And the "old saying": Don't believe everything you read online" holds true.
There's a guy "online" who "specializes" in restorations of classic audio equipment.
And he's got an impressive website for information as well as sales of parts "kits" to perform his "knowledgeable upgrades".
Even I, as a seasoned old tech was impressed, "to a point" with his "opinions".
However, he's not a tech, not like me, and his "restoration instructions" fail miserably in detailing some critical tube amp specifics that a real tech would obviously consider.
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