Just bought a 60's tube amp - advice needed

If there is only one 50C5, I would think it's more like a 2-2.5 watt amp, not a 25 watt amp.

The polarity problem is that the plug could be plugged in either way, creating a 120 volt difference on the ground line compared to other devices. I'm not too sure on how to fix it, and your amp be of a slightly unusual design, most of the schematics of amps I found using those tubes do not have a power transformer. If you could post some pics someone else may be able to help. In the mean time be careful.

egdinger is right on the polarity - IF it's a polarity problem. I kinda doubt it.

Old style plugs (like those from the 60s) can go into the wall either way, and modern ones have one 'leg' wider, so they only go one way. Some old tube amps have a polarity switch in the back, so you can toggle it.

The reason I doubt it's polarity is that your pedal probably isn't running AC current, right? So there's just a small battery, and it's also running on the same 'path' as your guitar - guitar into pedal, pedal into amp. Polarity issues raise their ugly head when you have two AC circuits - typically the amp and a microphone that's going into a PA - and you close the gap between the two circuits. My guess is it's a grounding problem.

The plate on the back is power IN, not power OUT - it's the spec for your 'wall current' to keep you from plugging it into the wrong source. I think that amp puts out somewhere between 5 and 7 watts.

Ok, it might be an a ground problem. I'm taking it to someone who will take care of this I hope. And it definitly sounds more like 5-7 watts to me. But why is it so big? Why the need for a 12" speaker?

Anyway to boost this or I am stuck with that unpowerful sound?

If you search around in this forum (Amplification) you will find some old discussions by Mr. Richochet et al regarding really old tube amps and dangers involved. Apparently, they used to make them without an isolation transformer, so that high voltages would show up on the guitar side of things. Since I don't have such amps, I did not follow the discussion closely, so my recollection is fuzzy. In any case, I think the summary was that this is dangerous and not easy to fix.

Just wait for Richochet to show up on this thread, I am sure he will eventually :-) Meanwhile, until you know what is going on, leave it unplugged. Hig voltages can be dangerous to your health :twisted:

Franky, the 50C5, 35W4 and 12AX7 probably mean that you have an AC/DC amp (which is what NoteBoat is referring to), meaning that it has all of the tube heaters in series across the power line with a voltage dropping resistor to make up the rest (50 + 35 + 12 = 97V, so there's another resistor under the chassis to dissipate enough power to make up the remaining 20V of the nominal 117V of U.S. house current.) Old power plugs weren't polarized, and could be plugged in either way. Like NoteBoat said, you've got a 50/50 chance that your chassis will either be connected to the neutral side of the power line and be near ground potential or to the hot side of the line and be around 120V. When you plug your guitar in, the outside conductor of the signal cable connects to the chassis, and the metal parts of your guitar will be at the same potential as the chassis. This creates considerable potential (little pun) for shock, especially if you sing into a mic plugged into a well grounded amp.

You can and should replace the old cord with a polarized one, making sure that the proper color coding is observed so that the white neutral wire is the one that connects to the chassis, and the black, hot wire is the one that goes to the switch. Then it'll be up to the approved safety standards of 40 years ago. Won't pass today's safety standards, and you can't make it pass. Plugging it into an isolation transformer is the only way to completely remove shock hazard, though it's a relatively low risk with a properly polarized cord. Isolation transformers are available from electronics supply houses such as: http://www.mouser.com/
http://www.tubesandmore.com/
http://www.alliedelec.com/

Thanks a lot all! I will try to add a isolation transformer but wonder if it's really worth it since it seems pretty expensive for the value of the amp.

And I'm knew to tube amps so it might look like a stupid question but it is possible to "boost" it so I can't take advantage of the 12" speaker? Is changing the tubes will significantly improve the volume level? As for now, it sounds good with no level variation or unwanted distortion, but it way too quiet for the size of it (16.5 inches wide by 8 deep by 20 high). Is this normal?

Thanks again. I will try to check old threads as well.

The RCA Receiving Tube Handbook says 2.3W is all you can hope for out of that amp. Changing tubes isn't going to make much difference, because 120V is all you've got for the plate and screen supply voltage. (Tubes don't make any power. They only control the power coming from the source, the power supply. The Brits have got it right when they call them "valves.") Yeah, it's not worth pumping lots of money into. It's just a fun little toy. Now, it may well be quieter than it should be for its normal 2.3W, if the 50C5 and 35W4 are weak. They're common radio tubes and not hard to find replacements for. Check that Tubes And More link above.

I sort of half read an article recently (I had something else going on and was not concetrating on the article, unfortunately) about old amps. The author was saying that 50's amps were still using a technology that got great clean tone and dynamics at the cost of volume. As guitar amps developed, the makers started to try and drag every bit of volume out of the amps as they could - deliberately sacrificing clean tone and dynamics.
Maybe yours is old school.

No mystery about the technology there. It's just about the drive levels to amp stages. Electronics engineers were taught that distortion was a Bad Thing. So the goal was to drive each stage with an input signal of such a level that it would not drive it past the point where clipping or significant nonlinearity would begin. In practice, guitar amps had to be built with gain/volume controls that would allow weak pickups to drive the amp to full volume, so hotter pickups could drive them into distortion, but that was considered a Necessary Evil. When guitarists of the mid '60s and later started wanting clipping distortion, the careful work the engineers had been doing to balance out the gain levels to avoid overdriving any amp stage excessively got thrown out the window, and we have all sorts of overdrive craziness now.