is there a schematic?

Solid state?...probably an XbbXXX to XFBXXX reverb. BUT...without a schematic we can't probably guess... Do you have one?

anyway Accutronics(Belton) aand antique radio supply both have charts to help with reverb selection.

The orientation and physical size matter too.

To get that kind of gain here in our studio...or in between that and bluesy I often use: guitar active pickups---->pedal of choice---->peavey TJraxx preamp or a KMD SS recording preamp----->Modded Valve JR to mike OR  Crate GX130C preamp ----DI to mixer board or to a homade TDA2050 power amp.    We have better luck using DI with heavy distortion...If not and miked we run a 20 second or so leader (quiet instruments...just hum and  hiss) at the beginning of the track to sample and then filter out later. I have used high powered amps in the studio....but in an "isolation" booth. To get mikes to tolerate high volume is very difficult. I almost never record with a high powered amp unless it's live and outdoors.

I Don't think most of the forum is fond of TDA7294 it has an awkward pin out for perf board and a nuisance for designing circuit board. I use some but you need good heat sink designs.

I also get circuit boards from hong kong. I don;t try and make them. I use them for repairs of hopelessly fried power amp pcb's when I repair others' stuff.

As for watts there is minimal difference of sound level from the 30 watts you can get out of a TDA2050 ( you need a LOT of heat sink to do this at 4ohms) the 60 or so from a 3886 or 729X. They are all just fine for home or studio/small gigs... From there I jump to 300-600 wats for gigs.

to double the sound level of a 60 watt amp you really need about 600 watts. (x10)

My stage rig...to keep clean at big gig levels I use two Carvin 200SX plus extensions powered by Peavey 160 watt ss power amps 2 vintage JCM800s for blues/dirty a peavey heritage (130 watts) and an Ampeg g212 (125) for steel and a Guild thunderbird 40 Watt (tube  1964) for some vintage sounds miked to the 1200 Watt PA system.

At home and studio I use a modded Epi valve jr ( about 3-5 watts) Fender FM15 and 25R (modded in the gain channel)(and through an old sound city 2X10 with eminence alnico speakers) for miked sounds and a Peavey (tube)TGRaxx and KMD SS preamps for DI.

There is a BIG difference btween gig and studio amps. TOO much power amp at home and studio at low level and your speakers are not putting out the sound they should be. OR you could have  low power speakers in your amps and you'll blow them if the amp is cranked when you play out. You CAN use something like a pair of eminence alnico 10s with the high powered amp in the home setting and get the 30-60watts worth of speakers in their sweet spot...BUT crank the power too high and you just got a 200 dollar junk pile.

My experience tells me a 100 watt amp is of minimal use at home and in most studio settings. Most lower power amps have crappy speakers. Put a low power amp into a godd speaker and you'll get a surprise.

Here's some examples May with little 10 watt amps  Clapton with a Champ (electric version Layla) With all the amps I have around I spend mopost of my work day playing through a Frontman 15 and a valve jr!

QuoteI have buy a book on tube amp on amazon, it is called
"the guitar amp handbook" by Dave Hunter.

That is a pretty good book...but doesn't give you overhaul advice...just background theory (abridged for musicians) It DOES have a project amp build...but he says if it doesn't work at first take it to a technician.

The book is worth having and reading though.


You would want to discharge each elemet of the can, and any other electrolytics just to be sure... only takes a few minutes..

Replacing wires make sure you have 600V wire...a lot of stores only have 300V hookup wire these days (like radio shack) buy several colors so you don;t get confused. And annotate a layout .


get someone to test your tubes before you buy new ones.

what ARE the two power tubes?

digikey mouser etc won't carry those. They are obsolete by today's designs

Look at http://tedweber.com/ They call them cap cans you might also look at antique radio supply  (tubesandmore .com)

can you still read the values on that can....You'll need to do that and make a little schematic before you take that off!

there may be up to 4 different capacitors in that can I can't tell for sure from the picture.

It would probably be a good idea to do a complete schematic and layout drawing before taking anything apart.

Look at the layouts and schematics on the tedweber amp kit site to see what I mean.

If you can't find a can that matches you COULD use some of the modern 2 capacitor cans like JJ makes...But you NEED a detailed schematic before you start modifying things.

weber and others have replacement cap cans DO not use NOS . There is a shelf life and they'll not be good.

Bypass? not sure what you mean  Standby? Standby switch goes on the HI V winding of the transformer. You WANT the tubes to warm up first.

Discharging cap. You discharge the HV from the caps at the cap to ground preferably through a resistor so no big arc. Carefully. Google the procedure.

EVERYTHING you do inside that amp before discharging you do with one hand...the other in your pocket. No rings or watches on your person either.

While rebuilding you CAN install a bleeder resistor. Take a look at power supplies of newer tube amps  (like a valve junior or such)
The amp will then start to bleed down as soon as you shut it off.

While working it helps dissipate if you leave the amp ON...and shutit off via a power strip.

There are quite a few tube amp hoby sites that discuss safety... You might want to research that a bit.

Oh and one more thing for the AMP's safety....Tube amps are opposite Solid state....they self destruct with an open speaker circuit. You MUST have a speaker connected if you power it up with tubes in it. (and yes to voltage gets high 3-500 even with the tubes out)

well a mixer Looks more complicated than it is...because it has sections that are repetitive for each channel.

It would be simpler to build it as a mixer PREAMP only than just use a power amp.  Here's an example schematic of a mixer amp I've been using for about 15 or 20 years...to see what you would be getting into

if it's basically the same circuit as the GX20M the later ones have TDA2050 chips...my grandkids have one...also the headphone and external speaker jacks get dirty and make it quit....completely  I usually spray some cleaner and then run a plug in and out several times (amp OFF).  Starts working again.  One of these days I'll change the Jack. FWIW the TDA 2050 does NOT "upgrade" the amp to more output as the voltage supply is still the same as with the TDA2040.

if you're talking about red and white RCA jacks going to a box in the speaker cabinet area....that is the reverb


If you look at the schematic...the preamp is everyting from the input to where the preamp out and power in jacks are... I don;t have one here currently but if you follow that schematic you can figure out which are preamp parts.

I use ebay and one local here in AZ sponsored by a TV station. I also get broken stuff from Guitar Center Tucson and Superpawn which although is in Tucson also puts stuff on ebay.

For people here that want low power home amps for starter project riceagemusic often sells lots of 4 or more guitars and Fender Epiphone etc paractice amps on ebay. Good source for starting projects. The also sell guitars that can be repaired...lot of broken headstocks bad neck sets etc. Titebond and homeade jigs and a steam jet can salvage a lot of guitars.

I for one can't afford the "American made" versions of some guitars I want to use (one's I used on my album would have cost 9000+. I learned to repair guitars and set up a shop so I could do so. I've made my steel and two of the guitars I record with so far.

That aside Carvin is mostly US made. Also Fender Mexican products are a good idea. Every Mexican that can get decent work is one less dying crossing the desert where I live. Had some knock on the door late last night apparently in trouble and asking for food water and for us to call the "migras" It got cold here in the desert this week.

The Fender amps or at least their chassis broken show up often on auction sites. I bought several for my grandkids often nothing to fix except jacks or blown output transistors.  (I've got an FM65 on the way now and have bought 25r amps for 9Dollars.)

QuoteThe Frontman might have these, if US/Mexican made, but if Chinese made (as the FM series) it will probably have a Chinese one.

OK I've mainly worked on more of the Tube amps...and Ilive near Nogales which is half in Mexico half US. It would probably be wise to check for manufacturer #s before ordering speakers though! I have run accross a quite a few "Hot Rod" and "VM" deluxes with fender special design labels that are identical to legend 12s. Could be a local thing?? The FMs I've come accross have all had speakers changed too though! Here...usually for Jensens.  course this is a predominately "country" area.

As Far as I have been able to tell....Fenders "special design" 12 inch speakers  (as in Hot rod deluxe etc) ARE emminence basic line AKA Legend.   Fender just rates them at lower wattage...Not sure but the Stock speakers night not be that different than a Legend.

looks like parrallel there series would be something like :   amp output+ ->+speaker1- -> +speaker2 - -> back to amp

actually you CAN make this a 2 12... Use something like Weber or Jensen mod low wattage 12s rated at 16 ohms in parallel
...you could also use 4 ohm speakers in series
just don;t use high wattage speakers...jensen mod 12-35s 16 ohm will probably work well.

however I think you'd be happier with the sound of something like a pair of weber 10F100t's  10" 15 watt speakers 16 ohm

but much more expensive.

You could probably get adequate volume out of a pair of Celestion Rocket 50s at 16 ohm too if you could find them.