Vintage Japanese tempo 35w4-50c5-12au6 help

[325chris]

Hey everyone Im new here and Im really having a tuff time with this little japanese amp i bought on ebay. So the story I got from the seller was the amp worked prior to him trying to install a new plug and after it was blowing fuses. So I got the amp and he had tried to install another two prong plug which I know is a shock hazzard so i went out to home depot and got a 3 prong and a installed it as well as all new tubes from a local tube shop here in denver. I made the assumption that he had wired the cord correctly so i did the same. Well the amp just keeps blowing fuses and 35w4 tubes so im currious if the plug is wired to the rectifier tube correctly. Im going to post pictures so hopefully you guys can help me out here cause im stuck on this one.

Thanks Guys

http://www.flickr.com/photos/80698781@N00/5688847698/
http://www.flickr.com/photos/80698781@N00/5688847670/

[Jazz P Bass]

Try this WidowMaker link: Widowmaker? | Lectrolab Guitar Amplifiers

[325chris]

I plan on installing a n68 isolation transformer soon but ive grounded the chassis already with a 3 prong plug im simply wondering if he had the 35w4 rectifier hooked up properly? neutral "white" to pin 3?

[Jazz P Bass]

I would not "ground" the chassis as yet.
Those older circuits used the chassis.

[52 Bill]

First of all let me say this. You are working on an amp that applies the full line voltage from the wall socket to the amplifier's internal circuitry. Unless there is some sort of protection built into the circuit it could cause you great bodily harm. If you really don't know what you are doing, please for the sake of safety don't work on this amp by yourself, or at least don't plug it in until you are certain that it is wired properly.

I can't tell much from your photos, but it looks like you are applying the full 120 vac to the filament of the 35W4, which will cause it to burn out. The filament ratings for the three tubes in your amp add up, so 35+50+12=97 volts, still too low for the 120vac line voltage. There should be some sort of power resistor in line with the filaments to reduce the 23 extra volts.

Here is a possible way it should be wired. All of your tubes have the filament on pins 3 & 4, so the black wire should go to the fuse, then the switch, then to pin 3 of the 35W4. Then pin 4 of the 35W4 should go to pin 3 of the 50C5. Then pin 4 of the 50C5 should go to pin 3 of the 12AU6. Then pin 4 of the 12AU6 should go to one end a large power resistor. The other end of the resistor should then connect to the white power cord lead.

Exactly how is your amp wired right now?

[325chris]

Thanks for the reply bill. I'm thinking the white(neutral) wire shore be connected to the other end of the heater string to complete the circuit is that correct?

[52 Bill]

Yes, but remember that you need a resistor to reduce the voltage down to safe levels for the tubes.

[325chris]

Thanks Bill for all your help. So the return on my heater string goes to the ground on my electrolytic cap so i need to put a resistor between my ground terminal on my cap and the connect the resistor to neutral (white). Does that sound correct?

[JHow]

This tube complement sounds like my 1950's RCA 45 rpm record player. Just for information, the heater string in that runs from the 35w4 to a 120 ohm ballast resistor (I replaced with 5Watter) and on to the heaters for the power amp tube and the preamp tube. On the record player, the heater string is not grounded to chassis, but returns back through a common wire. YMMV. One side of the line has the usual cap-to-chassis. The line voltage also goes to the rectifier plate (pin 5) to serve as AC input for what eventually become B+ at about 125Volts or so.

[325chris]

Jhow,

I believe our amps are very similar. On your 35w4 heater pin 4 does that connect to pin 5 (the plate) too?

[52 Bill]

I've looked at your photos 3 times now and I can't see enough there to tell how everything is wired. Most importantly the power switch. Maybe you can do a few more photos with better details? Or tell us how it is wired now.

The hot side of the line (black wire) after going through the fuse and the switch will need to go to pin 5 of the rectifier. If the heater string ends by grounding at the filter cap, the white needs to ground at this point too. The resistor must be added at the beginning of the heater string between the hot side of the line and the heater of the rectifier. The 120 ohm value sounds about right to me.

[325chris]

52 Bill brought the old amp into work today so I can work on it ill post some more pics up here in a second. Thanks a lot by the way

[325chris]

Ok here are pictures of the lamp and switch and how its wired to the 35w4
2011-05-12 13.34.13 | Flickr - Photo Sharing!
2011-05-12 13.31.28 | Flickr - Photo Sharing!

And I thought the heater return wire looked kind of funny because the wire insulation looked a little burned so im not sure if this is supposed to be connected here. used paint to make it easier to see

2011-05-12 13.44.14x33 | Flickr - Photo Sharing!

[52 Bill]

OK, the new photos helped a little. First off, the power switch needs to be rewired. It was originally first in line with the hot lead from the wall socket. I know this because the pilot lamp is wired to the fuse block and then to the rectifier tube, just like an old radio, used as a current limiter. The way you are wiring it, the B+ will always be powered live.

So the black lead from the ac cord should wire up to one side of the on/off switch. The other side of the switch then goes to the fuse block. The second side of the fuse block then connects to the pilot lamp and to the resistor at the start of the heater string. The second side of the pilot lamp should wire to pin 5 of the rectifier tube.

How is the switch wired right now?

How is the fuse block wired right now?

[325chris]

Ok right now the fuse is wired from the ac line black(hot) on one side on the other its going to the switch. Then the hot from the switch is wired to pin 5 and pin 4 the lamp is wire in to the same pins on one side and on the other its wired to pin6 the 6.3v heater tap.