vintage guild thunderbass tube amp

Does anyone know anything about this amp? What is the polarity switch and how do I know which way it should be? I can't get any sound out of the amp. Also there are two switch buttons-one for each channel-that have different circles in a row up and down. Any one know what those are for? Any info would be appreciated about this amp. THANKS!!

A picture would be handy. Since it's a tube amp you may need to let it warm up a while. The time varies among different amps.

Originally Posted by: nowonder11... What is the polarity switch and how do I know which way it should be? ...

The AC power plug is a simple two-prong thing, with no ground pin. The Polarity switch connects one side or the other to the chassis. This can be extremely dangerous! Basically, if you plug in your guitar, touch the strings and you don't die, it's probably in the right position. :eek:

In other words, don't play that amp until a qualified tech has replaced the power cord with a properly grounded three-wire cord, and disabled the Polarity switch!

Wow I hope he gets that one in time.

Yeah, the amp was originally working okay. And then it wasn't. I don't know if I touched the polarity switch and somehow messed it up. Now I get no sound-but I am wondering if I even have the speakers connected to it the right way. But yeah, I kind of thought the polarity had something to do with the grounding. So that is why I haven't touched the amp-just in case it is backwards. I just wonder if there is a way I could tell which position the switch should be in?

Originally Posted by: nowonder11... I just wonder if there is a way I could tell which position the switch should be in?

That switch connects the chassis to one side of the plug or the other, through a capacitor. This is intended to reduce the amount of hum. If the cap is healthy, it will work as intended, but if is shorted, and the polarity switch connects it to the 'hot' side of the plug, the chassis then becomes 'hot'. Which means the jack and the strings of your guitar are at line voltage. Touching anything that is grounded can then KILL you!

If you have an AC Voltmeter, you can check for voltage between the chassis and ground, before plugging in your guitar. Really, though, the only safe thing to do is get that two-prong plug replaced with a properly grounded 3-prong plug and cable. It sounds like you need to get the amp looked at anyway, so do yourself a favour. The life you save could be your own.

I didn't read this message in time. I bought a "modded" thunderbass at a pawn shop in the winter of 2010-11 with 2 prongs and what I thought was a killer deal! Sounded great. Had a "bunch of funny standby switches". No manual and only a wink and a nudge about the cool new amp i'd just bought. We never touched that polarity switch thinking NOTHING OF IT! worse it's already been re-covered in some kind of grillcloth on the aluminum chassis panel.

At practice it got EVEN Worse I had a buddy turn this thing on, while plugged into an old strat, (THANKFULLY WITH NO STRAP). He flipped all the switches like an idiot, after hitting the standby he flipped the polarity switch. It Knocked me on my ass, dropped the guitar instantly and the idiot was laughing at me! Pulled the wire out of the wall and we all shrugged it off, but I knew exactly how close that bullet had been from that day forward. Got it 3 pronged at a local repair shop. Creepily enough the amp tech died a few years later. totally unrelated but still the vibe has stuck with me all these years. I play it through a silvertone 8 Ohm 6x10 "Jack White Cab". Bought the whole lot for $270, and over 200 of that was on the amp. another $120 later i got it grounded. Sounds killer with this old tube ART DST-4 pre-amp, another banged up piece of gear from the web.

I learned the hard way, ALWAYS take it to a tech first!