DISCLAIMER: Vacuum tube equipment operates on very high voltages. 350-450 volts or more can be found inside a typical tube guitar amplifier. THESE ARE LETHAL VOLTAGES. Do not attempt to disassemble, repair, or modify any vacuum tube equipment unless you are qualified to do so. The purpose of this site is only to provide helpful information. The owner of this site is not responsible for any damage to persons or equipment resulting from misuse of this information.
Having fun with tubes
and a guitar ...
October 25, 2008
Hey, hey ... here my new 2 X 12 inchs speakers cabinet.
Click on any pictures for more resolution.
Cabinet dimension : 32" X 19.5" X 11" (9 1/2" on top)
3/4" thick finger joint solid pine box, solid pine rear panel by 3/4 inch thick
and 11 mm (7/16") Russian plywood (made in Canada...) front baffle.
Speakers are Alnico Jensen P12Q.
I did try the cabinet without the back, I like the close back for more bass.
Inspire by the Fender Bandmaster silver face monster cabinet,
the two speakers are isolated from each other by a solid pine separation.
This cabinet delever SERIOUS tone !
I'm woorking on the head cabinet now!--------------------------------------------
UPDATE - October 30, 2008
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A brand new toy, a "VALVECASTER" tube booster
here is the schematic : http://www.diystompboxes.com/smfforum/index.php?topic=63479.0
This one is running on 12 Volts DC, I add a LM7812 regulator to my DC adapter for precise 12 Volts on the tube filaments, without that regulation I had 14.5 Volts DC (under load) witch is too much for the filaments of the 12AU7 tube.
I had a pair of 100K Alps "Blue Velvet" potentiometers in stock, the Gain pot should be a 50K one, so I add a 100K resistor to the 100K pot (leg 1 and 3) that gave me a 50K pot out of a 100K one.
Here a break down of parts and cost of this tube booster :
1 - Hammond case : Model 1590B, 4.38"X2.4"X1.07". EACH $7.50 + $2.25 for paint = $9.75 U.S.
1 - 12AU7 tube Radiotechnique ( from Parts Connexion) $39.95
1 - 9 pins tube socket (from Parts Connexion) the brand is QQQ (aka 3Q) = $3.50
2 - Switchcraft jacks @ $2.25 each = $4.50 U.S.
1 - FOOTSWITCH, TRIPLE POLE, DOUBLE THROW (3PDT), BLUE (from Tubes and More ) $9.95 U.S.
2 - Potentiometers @ $2.95 each = $5.90 U.S.
2 - led lights @ $0.95 each = $1.90 U.S.
2 - Led chrome holder @ $1.15 each = $2.30 U.S.
1 - DC input power jack = $1.95 U.S.
2 - Knobs @ $1.50 each = $3.00 U.S.
3 - capacitors @ 1.85 each = $5.55 U.S.
4 - resistors @ 0.35 each = $1.40 U.S.
1 - 12 Volts power supply (1000 mA) = $10.00 U.S.
1 - LM 7812 Voltage regulator = $2.50
1 - LM7812 heat sink = $1.75
2 - 470uF 100Volts capacitor (for voltage regulator) @ $2.00 each = $4.00 U.S.
1 - board for regulator ($3.99 each, but I used only haft) = $2.00
2 - small capacitors for regulator = $0.75 each) = $1.50 U.S.
1 - Silicone tube from Home Depot for encapsulating the regulator = $6.00
Total cost : $117.40 plus money exchange (+/- 20 %) = $23.48 = $140.88
plus taxes (+/- 10 % = $11.74) , plus brooker fees ($5.00 USPS), plus shipping cost (=/- $20.00) = +/- $177.62 CD.
I also bought a MCF-9 (12AX7) series: 9-pin miniature-tube coolers @ $8.80 at Parts Connexion and the picture show a pair of "Blue Velvet" - Potentiometer, 100K @ $11.95 each = $32.70 EXTRA for this one !Update (Mai 31, 2009) I just try this tube preamp with my acoustic guitar that have a undersaddle transducer and it's working very well to bring the sound alive. Now you know !
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Here a few pics of the 5E3x2 that I (almost) terminated today (August 5, 2008)
Construction :
Power transformer is a 290DX Hammond 120 VAC 60 Hz. 325-0-325V @ 200ma 50V bias tap 6.3V @ 4A 5V @ 3A, Hammond replacement for Fender Super Reverb, Fender Pro Reverb, Fender Bandmaster Reverb, Fender Tweed Bassman, 125P5D & 022798. Equivalent to the Weber W022798.
Output transformer is a Hammond 1750M, 4,200 C.T. secondary 2, 4, 8 Ohms, Push-Pull 50 Watts, Fender General Replacement 125A13A & 022871. Equivalent to the Weber W404248.
Chassis : I used extrude aluminium angle 2 X 2 inchs that I found at a local home hardware store, 1/8 (0.125") thick, the top is made with a Lexan 6mm (1/4 inch) thick 18 X 8 inchs. The turret board is also made of transparent material 1/8" thick (not a very good idea ... It is hard to make modification on the board because the plexiglass don't stand the heat and it's melting very fast when soldering). I will stick with wooden board.
Here a link to the Schematic and Layout from Weber web site.
This guitar amplifier have been design by Bruce Collins from Mission Amp using the original 5E3 circuit modified with four power tubes 6v6 instead the usual pair of tubes found in the Fender Tweed Deluxe, power transformer and output transformer are about twice bigger than the original, and the power output should be around 25 Watts.
So far, I'm very please with the amp tone and performance except for the 100 Ohms/25 Watts dropping resistor that was running far to hot for nothing, that wass a waste of energy. I'm presently using an old 5U4GB RCA whitout that resistor and it's sound very good within desirable voltages, it wass a lttle "hot" with a GZ34 (402 Volts at first cap). I try a GZ37 with great success, but this tube is way to tall (5 inches over the chassis) so I will stay with a 5U4GB untill I try the fix bias mod (included on the Weber schematic). The turrets are already onboard for this option.
Fix (ajustable) bias conversion is done, now running with the GZ34 rectifier and I have now 375 Vots on the plates.
"Careful with That Axe, Eugene" this amp can play loud !
This is my third 5E3 amp, the other two are build pretty stock, this 5E3x2 is in a different class, I guess that the big irons are for something here, it is much more "fuller", my opinion is it dosen't cost much more than a regular 5E3 to build, but it will give you TWICE "every thing" ! This amp "SING".
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August 31, 2008This picture show my latest modification, I remove the 100 Ohms resistor on the center tap (this diden't increase hum or his), I removed the cathode bias resistor (and the associated capacitor) and I builded a netwok for fix bias (my power transformer have a 50V bias tap) using the specfications of the Vibroverb AB763 layout that use a 470 Ohms resistor, a diode 1N4007, 100uF-100V capacitor, a 10K potentiometer with a 27K Ohms resistor to groung (I had theses parts values in stock), giving me a range of about -45VDC to -53VDC mesure at the center leg of the potentiometer. To be able to set the tubes cathode at 0.030 A. I needed the 470 Ohms resistor a change with a 2.8K and I probably need a 3.3K Ohms (I end up with 6 or 7K Ohms. There is no more resistor running to HOT inside the chassis.
I found this info at web page : http://www.aikenamps.com/Biasing.html
And this interresting link about bias : http://www.faustineamps.com/docs/vt_58_um_b.pdf
NEXT MOD : the TONE STACK
As many peaples do, I don't like how the standard 5E3 volume pots react so I'm going to mod the volume / tone the BRIGHT channel using the s2 Audio Technology idea (that come from a combination of the Fender Brown Deluxe (6G3) for the NORMAL channel and the other, the BRIGHT channel, is from a Matchless Spitfire Amp, this combination will provide 2 totally different tones.
The needed 1 Meg dual TONE pot (ALPHA) for this mod
is available from Hoffman Amp @ four dollars a piece.
The two 200K (or 220K) resistors will drop the gain a little bit, so the use of a 12AX7 in V1 (instead of the normal 12AY7) will rebalance for the lost of gain. By the way, have you tried the new production Mullard 12AX7 / ECC83 ? This New Sensor's reissue Mullard at +/- $16.95 beat my NOS 12AX7 Telefunken that cost 4 times more, georgous tube for the price !
One of my two tubes have the cathode problem ... :-(
From : http://pages.prodigy.net/jimmcshane/tubes.htm
In stock!Mullard reissue 12AX7 long plates! Another new tube getting excellent reviews! One more fine quality
tube, and just $18.50 ea. or $39.50/pair. As usual, my price includes tests you pay extra for from some other vendors!
Important!! I have suspended sales of this tube until further notice. There is a problem with the cathode
activation and the tubes come out of the box very weak. Up to now, a special burn-in has solved the problem,
but now that's not working well either. I have about 20 tubes that are okay, but once they are gone I will not
be selling more until quality improves. I'm sorry to be the bearer of bad news, since the tube is great
when it's right. But it's not right at present.
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Reverb : Here my take for the 6G15 springs Reverb to match the Twin Amp, I will experiment positioning the Reverb chassis just under the amp in the same head cabinet.
Custom made wooden turret board made with KOA. Because the turrets are design to fit a 1/8 thick board and my wood is only .095" I add a stainless steel flat washer under each turret, the riveting process have been very easy with the washers. This chassis is made with two extruded aluminium angle bar (2" X 2" X 1/8" thick) that's DIY ... !
Some peaples are askim themself if I'm "silly" using wood as turrets board http://forum.metroamp.com/viewtopic.php?t=20727&view=previous&sid=f6d2fa96440e33bc4cb69e9c36f8a534 ... well I'm not "silly" and the idea come from Vintone web site : http://vintone.com/news.html and read this (from Vintone web page) :
Wooden? Circuit boards...... Why?
I read that a Famous Amp builder made his boards from wood. How Cool!! Then I actually got a look inside one of them to discover that the boards were actually Formica! A complete let down.So, I am now offering them as an upgrade option.
Is there any sonic benefit to using Hardwood? Probably Not.
Are they Cool? You Bet!!!!Hardwood was used in the early days when phenolic resin board was brand new and still too expensive. Look inside a very old phono or radio from the 20's and you are likely to see it.
The "silly" thing I did have been to use regular plexiglass as a board in my 5E3x2, it dosen't resist very well to heat when soldering, the wood board is much more resistant to heat. Next time, if I need a clear board, I will use Lexan instead of regular plexiglass, but wood is my preference.
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While waiting for the transformers, I installed the board in the chassis. It is hard to see, but I install a 1/16" thick plexiglass in the bottom of the cassis before inserting the boad, it make an isolation between the aluminium chassis and the turrets.
August 26, 2008Here a 25 seconds wav audio clip of the Twin-Amp with a bit of reverb,
Digitaly record with a MXL 901 condenser microphone throug a M-Audio Fast Track Pro interface.
Telecaster with a pair of Custom Shop NO CASTER pickups and a Weber 12" Vintage Series.
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Here the Reverb terminated ( August 28, 2008)
Note the layout, it is only two inchs high (2 1/4" at main transformer bell) by 18 inchs long,
wires are super short and there no hum or RF noise.
Specification of all tree tubes say that they can run in any orientation, so why not horizontal to save space.My idea to put the Reverb Unit right under the power amp wass not a good one,
there are some magnetic fied interferences between the two and the Reverb dosen't sound well so close to the amp. So I don't need this Reverb Unit since I already have an other one.
This one is now for sale for $300.00 (my cost price) including the tree spings Reverb tank
Just make a box and you have a old school (6G15) tubes Reverb Unit, point to point, for $300.00.Mail to : Jean GODBOUT (just change the (at) for an @ )
