Tube Amp Archive

Resistors are free compared to the cost of your time. Unless you don't have the right value available... That's the thing - it's really, really hard to say that one value is right, with a solid rationale for it. Electro cap leakages are ill-defined, to say the least. The manufacturers will only say...

The devil makes me want to say that if you need to be measuring them, and really ought to unsolder one end, why not unsolder >both< ends and put in new, tested, known-good balancing resistors? Resistors are free compared to the cost of your time.

Yikes! That style of PCB construction was what led me to set up the Workhorse amps with flying leads to the pots, jacks and switches, and also leads off to the tube sockets; and to do the mechanics so a repairman could get to -both- sides of the PCB without removing it from the chassis. I interviewe...

My understanding from something i read a while ago is that UF-type diodes do not need snubber caps, but I'm not sure if the voltage balancing effect would still be desirable. The need for snubbing comes from the semiconductor physics of ordinary rectifiers. Rectifiers have to have large-area juncti...

Yep, +1 to Martin! This brings up in my mind the question of why someone would put those capacitors there. I can think of two reasons off-hand. One is to "snub" the diode turn-off transient for non-fast/soft turn off diode, and the other is to force voltage sharing on the diodes during times of rapi...

Don't 50Hz transformers have a slightly bigger core ? In the USA, the vast majority of Fender amps have only a 120V primary. Can we assume they are intended for 60Hz only ? How much of a temperature change would you expect going from 60Hz to 50Hz ? 50hz cores are bigger, and it's a direct result of...

What in the construction or property of a transformer contributes to tone in a tube amplifier? You might like to read a series I started on the basics of transformers, here: https://ampgarage.com/forum/viewtopic.php?f=6&t=37347&p=467963&hilit=transformer+basics#p467963 Transformers can be modeled v...

Surplus? SURPLUS????? Those are your "Hey - I might have something in the bins that would work and I won't have to order stuff at midnight on Friday night" stock. Sort them into bins and types so you can find them, and only resort to getting rid of them if too much space is used up by the "ready spa...

Does the flashing still happen with > the output tubes pulled out? > only the PI tube(s) pulled out? > only the tubes before the PI pulled out? > all tubes other than the rectifier pulled out? It's a quick test, and should tell you whether it's a tube other than the rectifier tube that has an issue....

Get out Mr. Ohmmeter. Resistance from white wire to all the others?? My guess is it may be a tap, perhaps CT on the high voltage, or a bias tap. When you find out what other windings it connects to, switch to Mr. DMM and measure voltages. Carefully and safely... Could also be a wire to an internal s...

Near as I can tell from the schemos and J.S.'s comments, the FETs have nothing at all to do with the output tube biasing. They are DC isolated from the output tube DC bias by C122 and C123. Even if one of these caps were bad, the tube bias wouldn't go to -92V or whatever. Looks at first glance that ...

Ah.Thanks L.T.! @OP: An opamp is typically three stages internally, a differential amplifier, a voltage gain stage and a high(er) current buffer output stage. This is all obscured by feedback into a composite stage until such a frequency that the internal gain reduces and lets the internal stages sh...

yeah what you said...

It does make a kind of sense that similar sounds would need similar numbers of stages. The flaw in that line of thinking is that all stages are not equal, and even more so when the stages being compared are thermionic versus solid state. Tube stages, especially triode stages as used in guitar amps, ...

Side notes: Like steel, aluminum has various alloys and heat treatments that dramatically affect its strength, rigidity, and brittleness. The 606x series of alloys are the most common, and are a good compromise for general stuff, much like mild steel alloys are for steel. Steel and aluminum are (in ...