The Amp Garage

So I scored this used fluke MM and took some proper measurements.... One voltage on the tall PT is a bit odd.... The voltage from the wall is 124 VAC This is what I got... I have this wide one. I have a champ chassis that I cut to fit it. This one measures: From one leg of the HT to center tap 341V...

A 5Z4 is effectively the same as a 5Y3, so I don't think the tranny will support a 5U4 because of the excess current draw. Which lead are you using for the ground when you're measuring the 375V? That should be the one that's the center tap for the main winding. If you're measuring against anything t...

Thank you tubeswell. See what confuses me a bit is that Pin 2 and 8 are both filaments on a 5U4GB. Pin 8+ supplies 420VDC to the OT. So wouldn't Pin 2 which is tied to Pin 8 be able to supply 420V minus whatever resistor+cap combo needed to get the appropiate rectified voltage needed to the grid el...

The PI's in both of them are slightly different takes on a DC-coupled long-tail pair. The first one is truly DC-coupled w/ the 1M resistors feeding the CF setting the quiescent grid voltage for the PI. The second one isn't truly DC coupled because of the 22n coupling cap, but the isolated triode set...

That 100k + diode + other-stuff is the bias supply. The diode is backwards to create the necessarily negative bias voltage. With a bridge rectifier, the bias supply can't be connected that way, but must run through a cap. Some of the later marshalls have the same bias-supply setup. If you can't find...

First, if the 375 is measured w/ the tranny totally unloaded, it'll drop significantly when there's any load on it, probably closer to 325. (that's just a guess; others here will have a more accurate guesstimate) . That'll give you about 450VDC rectified (cap input load), which is pretty close to wh...

A bridge rectifier w/ a cap input load will give you a DC of approximately 1.4 * VAC. In this case, that's 375 * 1.4 or 525VDC. Once you have a load on it, it'll drop some. In any case, that's a pretty high B+. (a couple of EL34's :) ) If you wanted to switch to a choke input load, it'd drop to abou...

http://www.freewebs.com/valvewizard/bridge.html

You can do a hybrid bridge w/ 2 silicon diodes and a tube rectifier, but you can get the same effect w/ 4 SS diodes and a sag resistor.

Matt.

I bought this one a couple years ago. AES has several other designs. [img:311:500]http://www.tubesandmore.com/cemirror/inv/G-852.GIF[/img] This one is cool. [img:331:500]http://www.tubesandmore.com/cemirror/inv/G-869.GIF[/img] http://www.tubesandmore.com/scripts/foxweb.dll/catalog@d:/dfs/elevclient...

Yeah there are some cool old manuals there. This picture is from the RCA RC-12 book. I love it! You can see the various materials used in making tubes, no wonder the EPA has outlawed just about any chance of US manufacturing of vacuum tubes. I think I'm going to have that picture silk-screened on a...

I'm still looking. I know it's here somewhere.

I've got a schematic here somewhere, but it's taking some work to find it. As soon as I do, I'll post a link to it. Do you know if yours is an original or a series II or III?

Matt

tribi9 wrote:Ok, but out of the treble and bass pots only one is grounded so how would I go about making sure the "next stage has a good ground reference"

What would be the proper way to remove the treble and bass from the circuit?

That depends. What type of amp is it; or do you have a schematic for it?

So I rewired the AC cord according to the diagram and the amp is working again. One thing I want to mention is as soon as I started it the first time I noticed the amp was louder than before but the treble, bass, and speed and intensity for the Vibrato were not working. I opened it up and noticed t...

I know the Marshall guys over at Metro were saying the new Tung Sol reissue didn't do too well in V2. The tung-sol reissues along with the Sovtek 12AX7-LPS need an elevated heater supply for use in CF stages, along with other configurations such as cascode, SRPP, and even LTPPI if the tail resistor...