Output Tube Saturation BOX

[steve]

Jeff,

One Q- The OT puts out 190-0-190. So before any resistors in the power section, the voltage is 380? I'm going to start picking at that scab next...
Jeff

You mean PT (power transformer)? Which PT? The VJ power transformer puts out 0-260, meaning there is no center tap. The rectifier circuit used is a full wave bridge:

http://www.diycustomamps.com/images/...tock_schem.pdf

Look at the power supply, D1-D4.

To use a PT with a 190-0-190 secondary you would use a full wave rectifier (no bridge) and ground the center tap (the "0").


Here are a couple of resources for power supplies:

http://www.hammondmfg.com/pdf/5c007.pdf

http://www.bonavolta.ch/hobby/en/audio/supply.htm

steve

[zikaj]

Steve-
First, thanks for the ongoing support and information.

Yes, I meant PT. I have my Valve JR in pieces right now, and I was drawing out the schematic based on what I saw for ..(feel nerdy..) educational stuff. I was wondering why I couldn't put together the Hammond T numbers and those on the ValveJR T. The stock JR has the 260V on it, and I was perplexed. Now I get it.
Does this mean that after being rectified, the Hamond puts out 360? So figuring out the voltages and voltage drops across the dividers starts at those numbers?
Hey, I'm exponentially more informed about this stuff compared to just a week ago.
Going to hit those sites and read thru.
THX
Jeff

[steve]

Jeff,

Steve-
Does this mean that after being rectified, the Hamond puts out 360? So figuring out the voltages and voltage drops across the dividers starts at those numbers?
Hey, I'm exponentially more informed about this stuff compared to just a week ago.
Going to hit those sites and read thru.
THX
Jeff

I just took some measurements from my VJ. The raw AC coming out of the PT is 295v., not 260. This is because the PT is made for 115v coming out of the wall and I have about 125v.

The Raw B+ voltage is 367v. The peak voltage should be 415 (295 x 1.41) but when the tubes draw current, the voltage goes down. I put in a 1K, 5W resistor instead of the 220k for R10 to drop the actual plate voltage down to about 312. This keeps the EL84 from over dissipating.

One helpful tool is Ohm's Law. Do a Google search for more information on the permutations of it. When working on amps, you will use it quite frequently.

HTH,

steve

[Rob Mercure]

Herzog anyone?

Well, is no one gonna mention the "original" (or at least the first one that made it onto major vinyl that I know of) one of these? I believe it was Garnet Gillies who made the first one for Randy Bachman of the Guess Who (remember "American Woman" lead?) which only used a fixed resistor as a dummy load. I've made a couple of these over the years and they work fine once you've tweaked them for your particular amp - but they do require a specific guitar "touch" to get a long note sustain w/o a long noise sustain <grin> - yeah, I admit it, I'm a sloppy player but "ethusiasm" has to count for something.

Rob

[Steve Conner]

Yay! So this is the thing that put the Overdrive in Bachman Turner Overdrive?

[Rob Mercure]

Steve,

Yer probably right but BTO was a bit "over-something" for me - somehow lacking the, hmm, guess it was "innocence" (naivete?) of the Guess Who. Going from anti Vietnam war music to "taking care of business" was a bit of a let down to me.

Rob

[zikaj]

Back from the dead! Resurrecting an old post here.

I was googling Power Tube Saturation and I came across my own post here from two years ago. I was tinkering around with my first tube amp back then - a valve Jr. Trying to get output tube saturation in a box and use the signal to drive a line out.

Well, it took two years to get it done, but I have a follow up- Line Out with a Weber speaker motor for a load. (duh...why did it take this long?)

I pulled out my 'project box of parts' last night and cobbled together a voltage divider w/ a 5K pot to drive a line out. Loaded the amp output with the speaker motor, and turned the amp main volume up to 11. I used a moderately modded Crte V18 - (one of those mods was adding an "11"...)

I rebuilt the preamp to run cleaner than stock- tone to come from pedalboard for the most part. But the 2 EL84s when cranked are TOO LOUD , especially in my home. So dimed the amp and ran the line out to a solid state amp & 2x12. Fantastic.

I had not really heard that sound before out of the amp. By the time I got it up enough to drive the output tubes, stuff was falling off the walls. So it wasn't...enjoyable...to have it up that loud. I put a H2O Monty Allums modified BD-2 in front of it and was amazed.

I feel like I made some kind of low-volume tone break though. I could kick myself in the arse for waiting this long to do such a simple thing.

[Gtr_tech]

I was *just* gonna bring that up. The whole "herzog" thing came from Bachman using a Champ in front of another amp input without a dummy load. He kept blowing up the champ and consulted Gar Gillies to find out why. Gar basically told him he was a dumbshit for doing this, since he was diming the little amp unloaded for the most part. Gar built Bachman a Champ with an internal dummy load....problem solved. The name came from a book Bachman had with that word handwritten on it.

[zikaj]

Wow. Just looked at the dates. Before today, the thread was last posted to on 1-22-07. Almost 3 years ago.

And so now I have some question with where and how to send the Line Out signal... Time for a new topic.

- On the BTO topic- I ran that old Valve Jr without the speaker load once by mistake. Thought it was strange that the OT was making guitar noises...and then no noises...