Interesting tube amp articles

Is the Vox AC-30 really a Class A amp?

• http://www.aikenamps.com/VoxAC30classA_2.html

Tremolo design options

1. Several different power-amp bias modulators: http://www.lynx.bc.ca/~jc/tremoloCircuits.html
2. Input stage bias modulator: http://www.lynx.bc.ca/~jc/supro_s6616.pdf This one is interesting because the LFO drives a source follower connected to the cathode of the input tube! Have to look at that carefully.
3. Typical Fender LDR tremolo. extensive analysis: http://terrydownsmusic.com/technotes/vibratocircuits/tremolo_circuits.htm

Building amp and speaker cabinets

Working with Tolex

http://steelguitarforum.com/Forum11/HTML/008611.html

Some plans for different cabinets

• AX84 1x12 speaker cabinet http://www.ax84.com/static/corecabinets/AX84_1x12_Cab_09.08.03.pdf
• AX84 head cabinet http://www.ax84.com/static/corecabinets/AX84_1x12_Head_Cab_090803.pdf

Tube amp resources and web pages

Comparison of various tone stacks

http://amps.zugster.net/articles/tone-stacks#BlondeTwin

Yet another guy who's made a bunch of different tube amps in his spare time.

http://www.naturdoctor.com/Chapters/Amps/

AX84 - the cooperative tube amp project

http://www.ax84.com/

Tube Amp Schematics and equations

http://www.aikenamps.com/Equations.htm

DIY Tube Guitar amps

http://www.diyguitaramp.com/

Tube guitar amp schematics

http://www.drtube.com/guitamp.htm

Fender and Ampeg schematics and layouts

http://www.turretboards.com/schematics_library.htm

MOSFET tremolo circuit

http://www.geofex.com/Article_Folders/sstremolo/sstremolo.htm

Terry Downs technical notes

http://terrydownsmusic.com/technotes/TECH.HTM

Digital effects unit for tube amps

OK, there's no such thing as a special purpose digital effects unit for tube amps.

First I need to find a place in the amp that can work as a mixer stage, as close to the power amp as possible. Then I need to attenuate whatever the signal is at that stage down to the correct level so as not to fry the input of the effects stage. Following the effects unit I will need a gain stage to take the effects level back up to whatever it was coming in from the previous gain stage.

Thinking about using simple resistor divider on the FX input and a MOSFET gain stage post FX.

Maybe this is best done with an amp using a long-tailed phase invertor since that can act as a mixer stage.

Speaking of the effects board itself I am considering the Spin FV-1:

http://www.spinsemi.com/knowledge_base/demo_board.html

Here's a page describing this board used in a guitar amp. I would prefer not to run the entire signal through it - just the effects send, keeping the dry signal intact.

http://www.spinsemi.com/guitar_amp_application.html

My third tube amp project

eBay yet again!

Up for bid is a mid 1950s Radio shack of boston AF tube mono amplifier. Unit uses 2 6v6s and a 6sl7 for audio . I have had it up and playing for a few hours and it sounds quite good. Now keep in mind this is a 55 year old piece of vacuum tube equipment so it will probably need cap replacement and service. Nice little amp, has phono/mic input as well as one marked radio.

2 x 6V6 gives us a push-pull output, but 6SL7 is only a dual triode. Assuming that one half of this is used as the phase invertor for the power amp, it leaves only one stage of gain for the guitar, which is not very exciting.

May need to add another stage or even go over to 12AX7, although the idea of trying the 6SL7 which seems unheard of in guitar amp designs, is, well... interesting anyway.

======================================

The Fender Deluxe 5C3 schematic below shows a 6V6 pair driven by the 6SC7 phase invertor.

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj1aM0-yvJiCCUSLFM24K_Ley4pRZ4-S2ZWPuY8ZeJJ5XA4nnKe2VNv1FeRH_G7Nm9YYbaYdTDemBKOHz1kgvQuFbd6Uomhg3Kzy2WyZS6rlMmINh4sFmQMwfraV5rbEDI0zgLDeav1KYg/s1600/fender-deluxe.jpg

I'd like to use the Fender 6G7 Bandmaster bass-treble tone circuit as shown here (see non tremolo channel at bottom left).

http://www.turretboards.com/layouts_schematics/fender/schematics/fender_bandmaster_6g7.gif

This schematic shows an Ampeg Jet amp using the 6SL7 as one channel gain and tremolo.

http://unofficialampeg.com/schematics/j-12-a.gif

Here's an interesting amp with a switch to vary the treble boost in the first gain stage and also bypassing the power amp cathode for a Vox/Fender variation

http://angela.com/angelasupersingle-ended6v6guitarampproject.aspx

My second tube amp project.

The eBay description:

Here is a vintage mono WEBCOR TUBE AMP PROJECT, early 60's era, uses a pair of 6V6 power tubes, 6X5 and a pair of 12AX7 tubes, came out of a tape recorder, chassis measures approx. 15" x 8", there are 2 model numbers 2791 and 2792, you should be able to find a Sams if you need a schematic, it has a couple 1/4" phone jacks on the back panel, takes a detachable power cord which is missing, this is not a "plug and play" amp - you will have to sort out the controls and loose wires, so you should have a basic familiarity with tube amps, I do not remember if this amp worked or not, it may or may not work, tubes have not been tested, it would be a good idea to replace the caps seeing that they are 40-50 years old, I can't guarantee anything though since it is old equipment, you get what you see in the pix, this would make a cool vintage guitar amp or whatever else you have in mind, selling as-is

$59.


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It being a tape recorder there are probably a lot of extraneous circuits such as oscillators etc. that I don't need. Pair of 6V6 at least means we are in push-pull territory.



Would like to do something in the Fender Deluxe category here. Again looking for a three-band tone control and adding tremolo if it sounds good. I have an extra triode stage I can use instead of having two inputs.

http://www.turretboards.com/layouts_schematics/fender/schematics/fender_deluxe_5c3.gif

Steve tells me that a Blackface Princeton also has 2 6V6's and I think I found a schematic which proves him right. So

then the question begs what's the diff between this Deluxe and the Blackface Princeton?

Here's the Blackface Princeton Reverb schematic, looks dead on what I'd like to do. Although I am tweaked enough to want the digital effects using on it.

http://www.turretboards.com/layouts_schematics/fender/schematics/fender_princetonreverb_aa1164.gif

As it appeared on eBay

First tube amp project

Christmas, 2010

Starting with this thing I got off eBay:

MAKE: WEBCOR

MODEL: TP4905-1A
WEBCOR MONO

Here's a picture of the schematic.

1/2 12AT7 in the front end. This being a dual triode there is another half available.

It has a single ended output using a 12AB5 pentode. Not much info available on this:

http://www.radiomuseum.org/tubes/tube_12ab5.html

I want to adapt this to Fender Champ/Supro specs, possibly using a 2 or 3 band tone control. If it sounds OK I'd like to put a tremolo circuit into it.

Fender Champ

Gibson GA-5