The Amp Garage

You could also use a pot, as long as it's in series with a resistor that sets your minimum value. I do this a lot on amps because it gives great control over the headroom of the PI.

Merry Christmas, all! Santa was good to me this year and brought a Strymon Mobius! Woohoo! In other news, I finished my Bassman 100 head to Plexi 50 conversion yesterday. I am extremely happy with it. It rocks and has virtually no 60 Hz hum. I'm gonna swap peanuts till I find some with less hiss and...

I had wondered if the tank had come from an organ, and the resistor was meant to protect the transducer from too hot a signal. But I just don't know. I do know it has an effect on the verb, though.

A client of mine dropped off a bunch of old reverb tanks, some missing springs, some of questionable function, etc. One of them was a Hammond branded tank, same impedance values as Fenders normally use. This tank had been hard-wired into something (he couldn't remember where it came from). It turns ...

Brian's main guitars are Teles and an SG with Burstbuckers. The MV lets him dial in what he needs for the venue. Most venues want less and less stage volume, so a good MV is pretty much a must these days.

This year has seen load of repair work, so building hasn't been a priority. But, given the economy, only one client has really wanted a build. Here it is. I used Princeton Reverb size chassis and up-powered iron from Allen amps and put them into a PR cab the client built. He liked the Brownface look...

I do, but a US 220V outlet is not the same as a European outlet, since an appliance outlet uses two legs of 120V. If there's a way to wire up an outlet that would work, I'd sure appreciate the advice.

I have a client who wants to send his Silverface Vibro Champ to a friend in Spain as a gift. It appears that the amp he has agrees with the schematic at this link: http://www.webphix.com/schematic%20heaven/www.schematicheaven.com/fenderamps/fender_vibrochamp_ab764.pdf I am reluctant to convert the a...

The smaller cathode bypass cap can help tame bass response if the amp is too woofy.

The bigger bias cap value can yield a quieter bias supply.

I haven't posted in a while, since I'm not building much. I've been doing a lot of repairs, though. Most of that is pretty routine stuff, but every once in a while something odd comes across the bench. I picked up this silverface Princeton Reverb today. The owner was unhappy with it after a tech in ...

I worked on an old Teisco amp that had two pilots. One (white) came on for power up, then went off when flipped to standby, when a second, red one came on. When I first rebuilt this amp a couple of years ago, I found a rotary switch that allowed the original functionality. Turns out it just wasn't m...

Nice build.

You may be way ahead of me on this, but those little eyelets on that type of board can be loose enough to vibrate. So when I've used that style I put a bit of solder on every one of them so the tab is soldered to the eyelet. Chasing down a mystery buzz is just not fun.

That screen resistor helps restrict screen current flow. In pentode/tetrode connected amps, that resistor can be fairly large, say 1k5 or so. In most triode connected amps, like a lot of hi fi stuff you can look up, smaller resistors are used. Common values are 100R or 300R.

Dr Z, Thanks for that breakdown. Obviously, you have a lot more expenses than most of us: shop rent, insurance, employees, advertising, dancing bears on employee birthdays, etc. Since my building is in my spare time, I don't have all those costs. I have been--generally--charging about twice my parts...

The dual gang pot is, indeed, the MV. I use a 250K value. In theory, with cathode bias tubes you could go as high as 1M, but I think that would just end up sounding mushy and over compressed. However, I haven't actually tried it, so it may be worth an experimental installation. What's the worst that...