Priceless Amp Restoration

03/11/2026

02/08/2026

11/29/2025

Tube Matching.

I don't think I ever posted my tube matcher I designed and built back in 1999, but here it is in case someone else would like to build one.

We can pay a little extra for tube burn-in and matching when we buy power tubes from our favorite supplier, but what do we do when we have used tubes and want to know if they are matched and will they bias up ok so we can use them in our amps? Of course you can use your guitar amp to make this determination, but you certainly don't want a tube burning up in your vintage amp just to see if they are good and are matched. A failed power tube in your amp can take out the screen resistor, melt the tube socket and worse case stress or damage the power transformer or output transformer or both. Yikes. Well lets build a tube matcher with protecting fuses.

A picture is worth a thousand words, so look at the posted schematic and you should be able to figure out what I did. This design is best used with a Variac. A Variac enables you to slowly and safely bring up an unknown tube or to take measurements at different B+ voltage values. Thus a separate heater transformer is used to keep a constant 6.3vac on the heaters. If you were add a another separate transformer for the bias voltage, you could literal perform an IV curve trace matching.

Other features of this design are:
Separate fuses
Can monitor all voltages
Variable bias control
Can test up to 4 tubes
Selective tube measurement via a selector switch
Idle (bias) current measured with low voltage DMM
Can test 6L6, 6V6 and EL34 tubes

03/23/2023

Got tone?