Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jaymez78 on May 09, 2016, 03:09:27 pm
-
Hey Guys,
I'm new to the forum here and just began working on building tube amps. Been playing tube amps for years but recently built a Champ Clone and I found an old Radiola 80 radio. Question is has anyone here converted one to a guitar amp before? Is it feasible or just a waste of time to try? I have been searching the forums for a discussion on converting old radios to guitar amps but haven't found anything. If I missed that discussion than please direct me to it thank you all.
-
Not as old as your radio, but I did a 1941 RCA Victor Model 28T Conversion to Ampeg J12B Jet. All I used from the radio was the cabinet, chassis, and power transformer. Here's the info...
http://sluckeyamps.com/RCA/RCA.htm (http://sluckeyamps.com/RCA/RCA.htm)
-
Welcome to the forum Jaymez!
If you can find a schematic online for the radio that can be helpful.
I too was intrigued by this conversion idea.
As I've learned more, it becomes obvious that guitar amps are different than radios.
Now I see the best plan as stripping the vintage parts from the radio,
and reusing them in a proven guitar amp design/layout that you like the sound of.
The PT and tubes are often reusable. The case/chassis/OT maybe not.
It all depends on the model you have and the parts it contains.
There are reusable parts in most, that if you buy them cheap enough ($20 or less, free is best) make it worth the trouble to me. :icon_biggrin:
-
... I found an old Radiola 80 radio. Question is has anyone here converted one to a guitar amp before? Is it feasible or just a waste of time to try?...
Do you have a schematic for it? If not, you may be able to get one emailed from http://www.radiomuseum.org//r/rca_radiola_80.html (http://www.radiomuseum.org//r/rca_radiola_80.html)
Did the radio have tubes in it? Does it seem to work at all?
From a quick glance at the Radio Museum site above, it appears to use some very old tube types, which may be difficult (and/or expensive) to find (Type 45 (aka 245, UX245, etc) jumped out at me as your likely output stage). That said, every radio receiver already has an audio section in it. So theoretically, all you need to do is find the right point at which to inject your guitar signal (though you may have to re-work one of the radio- or intermediate-frequency stages into a preamp gain stage to boost the guitar signal).
-
The question as always is input labor, time, and $$ versus usefulness of output result. Maybe if this is your first project, you'll have so much fun doing it that none of the above will matter. Maybe not!
Some of us scrounge old gear and try to convert it into guitar amps. Some folks never do this. Although I scrounge, it's my opinion that such projects almost never turn out as nicely as buying the right chassis and all new parts.
Most tube equipment, with the exception of powered radios (by powered, I mean having a real output section aka 2 qty 6V6 or 6F6 (as you might find in yours) will not make enough B+ using the existing transformer to really make a Champ or a Princeton. I have some nice tube based Winegard video line amps, for example. Cute little things, would be perfect for a little Princeton and the power transformer is exactly the same size. Guess what? The PT makes a grand total 120 volts DC on a good day and you need 350. Because back then, a video signal was 1 volt driving 75 ohms (about .013 watt) and that was all the output section had to swing. And ANYTHING more than that just was wasted heat for the user and extra cost for the mfr. Test equipment is like this too. Many many pieces of test gear can make 250 volts and drive 4-5-6 little tubes talking 25-30 mils = 7.5 watts. Oh wait, we have to light up the tubes.....
It is kind of rare in my experience to adapt from existing gear a thing that 1: works, 2: sounds decent, 3: can be carried around without breaking and 4: is as convenient as a combo (meaning speaker and amp in one box)
I never ever want to discourage anyone from trying these things. But when I add up the parts cost of say a Princeton Reverb and add in the time to build it....it just doesn't make sense. Forget not that maybe you do not want to buy a clean used Princeton Reverb today for say $600. You could buy that amp today for $600 and sell it in ten years for $600 so really....they don't cost anything.
-
All,
Thank you for the input. I have found the schematic for it and it did work the last time they tries to plug it in. Needs a new power chord now. looks like mice ate it. Thats not a problem. it does have all the tubes and they are 245, 224,227 a lot of old tubes but I have found some online. All RCA's ST shape tubes. From what I've found the power tubes don't use as much B+ as typical Guitar Amp power tubes ala 6v6, EL34 ect. Some where around 200V for the B+ so I would need to use those tubes for sure. Some kind of old full wave rectifier. Is there any use for the RF tubes in a guitar amp? As far as making money that isn't my objective I just like learning how this stuff works. it appears to be a Push Pull but I don't see a phase inverter so not sure how it works yet. I'm picking it up tonight and ill wire an new chord on it. Plug it into my dim bulb tester and see what lights up. Thanks again.
-
The phase inverter is a transformer.
-
Took it all apart last night and wired a new power cord on it. I used my dim bulb to fire it up. The light on the dim bulb came on and no heaters light up in any of the tubes so I have some short somewhere. If I pull the rectifier tube the bulb will not light up. put the rectifier back in and pull either power tube and it does light up, all the tubes use 5 V or 2.5 V for the filaments. I didn't fins a schematic only a layout and there isn't much you can see in the power amp chassis, all point to point wiring with no caps and one resister that I can see without taking all the other convers off the various components bolted to the outside of the chassis. Probably not worth the trouble.
-
Most "consumer grade" wiring from the 30's looks like something from another planet to me. I suppose there are folks who look at the innards of a 1950's TV set and feel the same. That's sort of what I grew up on. There are people who make these things work; the stuff from the 20's & 30's. (and earlier)
-
Probably not worth the trouble.
That is what I have mostly found.
Usually the innards are in rough shape from age.
Mold, dry wire rot, caps all shot, rodent damage/droppings etc.
Now if you can find something that has a PP 6V6/EL84 output section,
then even with mold/rot etc, you can strip the PT/OT/tubes for a real amp build.
Even a SE 6V6/EL84 output section can work for a little 5 Watt amp.
You take the transformers, get a guitar amp chassis with new sockets/wire/components,
and then build a proven guitar amp circuit/layout.
That is what I try to do now.
No more trying to convert a fragile/decaying radio carcus into a guitar amp for me. :BangHead: