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Vintage threads from the first ten years

Davis 106 Pa Head

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3/7/2000 8:47 PM

Davis 106 Pa Head

To whomever was drawing the schematics up for the Davis head, I lost where yoou had hte pics for this at. I would lke to look at them again. With your pics and with what left of the guts of my amp, I'll be able to help you with drawing out the schematics... I did the stupid thing of stealing components w/o sktching out the schematics first *laugh*
Gino

p.s. I love the fact that i'm not the only one who uses the mid-air soldering technique when I have to!!

3/10/2000 6:44 PM

Self-inverting EL84's, etc.

Hi Folks:

Well, I did get this amp drawn and it is interesting with the self-inverting EL84's. Also a pretty cool Low Impedance Input and minimalist tone *stack*.

Didn't try it yet but as soon as I find that 6CA4 I'll variac it up and add some voltages to the drawing if all is well.

As a reminder, the 6EU7 is supposed to be identical in electrical properties to a 12AX7 except for the heaters and pinout.

The 6CA4 functions similarly to a 5volt rectifier except that the cathode (source of HV DC) is isolated from the heaters, so it can use the same heater supply as the rest of the tubes, and does not need a separate 5volt winding.

http://members.aol.com/mbsetzer

Anyone who wants to post it to the ampage schems, or if SteveA is interested in putting at blueguitar, be my guest, I won't be able to keep it at AOL forever.

there is a GIF and a PDF version, I ususally have better luck printing the PDF's by clicking the print option to fit it to the page.

If it operates, something tells me that the Booster Out could be an input instead, depending on what you hook up to it ;-)

;-)

I might not change anything until I try it as is and see how it sounds, just have to dig in to the CB radio surplus and get a screw-on microphone connector to make an adapter for a guitar cable. Two gain stages and a pair of 6BQ5's shouldn't be too bad.

If I did decide to change it, I would probably go clean-slate, and just think of it as transformers & tube sockets with three 1Meg Audio pots that could be changed in value & function too. Maybe wire silicon diodes underneath and use the 6CA4 socket for a different tube as a driver or trem. Or go single-end using only one 6BQ5, replacing the other one with a 12AX7 for more serious gain. Or both. Maybe even reassigning the 6BQ5 to the former 6CA4 position. If I was real ambitious I would even consider rewiring only the power tube sockets to be 6BM8 triode-pentodes for more gain after converting the second preamp triode to a split-load to drive the 6BM8 triodes separately.

Anyway, if it comes to life as is, I'll try to get some sound clips posted.

Good Luck,
Mike

3/10/2000 7:10 PM
Rebel420	I owe you a proverbial beer man!! I'm probably going to make a 'mini-plexi' out of mine THa t output tranny is some seriously hefty iron! I blew a chance for another one of these off of Ebay a week ago for $10.. Thank you again!

3/10/2000 8:05 PM
Rebel420	another intersting thing I noticed, was putitng the center tap of the filament to he cathodes of the 6bq5's for a reference instead of straight to ground...

3/12/2000 4:50 PM

Hi Rebel,

Well, there was at least one error on the drawing. The first preamp section gets its high voltage from the screen supply, not the plate supply that I have drawn. Still not like a regular guitar amp.

I did one take of an MP3 and posted it at:

http://members.aol.com/setzeramp

Actually only the first half of the file uploaded before I lost contact with aol, the unreliable. Just as well it was lame picking, plus I can't yet edit out the first part where it's blank while I walk from my desk to the lab, shut the door, pick up the guitar and start.

This was the amp stock, I didn't have a CB mic to fit, used a screw-on probe connector from a surplus probe from an old simpson VTVM. With a phone jack on the other end, plugged the guitar straight into the mic input. Both volumes are interactive so I keep the MUSIC knob maxed always. Start with the MIC knob halfway up for a few clean notes, then fading sustain as I dime the MIC control & torture my speakers ;-)

;-)

Ears too.

It is a little unstable at full volume but I thought it had potential, so I started tinkering with the circuit, I'll let you know when it's an actual guitar amp. I decided to leave the tubes as is and let the 6BQ5's self-invert, changing relatively few items and expecting it to be even better as an office PA than originally.

Until then I did get the stock voltages and as soon as I get more time I'll update the drawing and correct it as well.

Good Luck,
Mike

3/13/2000 1:22 AM
rebel420	very cool... kinda wish i woudunldda modified mined instead of stripping it for parts.. very cool, 'british' type sound!!! thank you again for all your help... will keep the board posted when i have my mini-plexi in the chassis...

3/13/2000 9:35 PM
Graywater	Re: Self-inverting EL84's, etc. MB, Just had to take a peak at your "self-inverting" output stage and I believe the conventional term is an "anode follower." Anode follower phase inversion usually preceded the output stage and this design isn't common - kinda makes you wonder about phase related products in the output tranny (love the neon screen supply "regulator"). GW

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