The Amp Garage

We say diode rectified gives 1.4x AC voltage as the DC, but this is unloaded. My rule of thumb for valve amps incorporating the first filter cap ripple has always been 1.32x. 330 x 1.32 = 436VDC so in my books you're spot on where it should be. Decent rule of thumb for tube rectified supplies. The ...

Cathode biased outputs ride with their grids at a different DC level than fixed bias tubes. Is it possible that the capacitors separating the sets of grids are leaking? A fully cathode biased output tube runs with its grid at 0vdc; a hybrid cathode + fixed bias tube runs with its grid at between 0Vd...

In general, a film cap of the same capacitance and voltage rating will be bigger than an electro. This only gets fuzzy where the cap rating is small, and the packaging case and leads, etc. are a bigger part of the entire package than the working capacitor plates and insulator. If it was the other wa...

I have not tried it myself, but have taken note that often sag resistors for SS rectified amps are inserted between the transformer & the diodes. They are indeed, but they don't have to be. Ignoring the heating/power dissipation considerations for a moment, it makes no difference at all. In a full-...

Yeah, the net result of my simulations is that motor tun caps are way, massively, overkill for any normal service considerations. I have not dug deeply into Solen caps, but even ordinary box caps are fine for all but the first filter cap. Film caps with some special-ness should be fine if they can b...

I think you're losing it in your dropping resistor. 750 ohms seems pretty big there. How did you come up with that value?

I started to get out the spreadsheets, but the dropper is where I'd look first.

You beat me to it sluckey. Drop the dropper.

On a more tech-ish turn, I decided to see how bad a real test case for film caps in an amplifier would be. Like many others, I had a premonition of metal cans coating the whole chassis. Turns out, not so much. I picked a Bassman 6G6 as a test case, for no reason other than I had the schematic. It us...

As a general note, new-manufactured LDRs have become problematic worldwide. Environmental restrictions In the manufacturing countries - first world and China, for instance - have make the use of cadmium sulphide and cadmium selenide compounds illegal. Even where they can be manufactured, they're ill...

Think about the Vintage Voltage Adapter :D from geofex: http://www.geofex.com/article_folders/vintvolt/vintvolt.htm . It's a common problem, and a smallish (compared to the PT) auxiliary transformer can fix that without a lot of tinkering, no variac needed, and without dissipating the power spent in...

I just don't see the value of going to all the trouble. I'm not going to be around in 50-100 years and I really don't care if the amp breaks when I'm dead. OK. It's not for you. This was never meant to be for every amp and for everyone. You may remember the auto industry's concept cars. These were ...

In a tight chassis they just can't compete with the high storage density of today's electrolytic caps, which have gotten quite small. Yes - they are much bigger than electros, although both film and electros have gotten much better with materials from the last couple of decades. I did ... um, autop...

How much life is enough life? Indeed. I think that most guitar players would not like their amps to last less long, though, no matter how old they are. There is a vocal "older is better" lobby too. That's hard to square with the people who seem to think that replacing even one original-manufacture ...

I am partial to this bias circuit which uses the R in the CRC filter to drop the voltage. It fails to the raw bias voltage (on C1) in the event of a bias pot failure, either from the wiper losing contact or an element cracking. A member here recently had the element crack at the rivet on the wrong ...

I guess I really need to start calling it the Immortal >>Tube<< Amplifier; The Peavey CS800 may have the unqualified "immortal" tied up! :D From the other thread on why Fender used an electro in their fixed bias supply (here: https://ampgarage.com/forum/viewtopic.php?f=6&t=38036&start=15 ), I think ...

That is indeed the question! What problem needs solved? I was solving the question of how to convert the electrolytic filter cap in the bias supply over to film types, which have a hugely longer usable life without replacement. This is a problem of practicality: how to find a suitable replacement th...