Need Help! 50w kit

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micahnix1
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Need Help! 50w kit

Post by micahnix1 » Thu Jul 27, 2017 5:59 pm

Ive got my 50w kit all assembled and all voltages are correct everywhere, but on channel 1 all I get is a hum when I turn the volume up, and there is a clicking sound almost like a heartbeat. The volume works on channel 2, but I'm getting an awful, unnatural sounding distorted tone.
I'm using classic tone trannies. Everything from PT seems to be in the correct place and grounded properly. Output is purple to 16 ohms, orange to 8 ohms, yellow to 4 ohms. I've fiddled with the impedance switch to make sure it's in the right spot. Just re-wired inputs to make sure they're correct.

Triple checked all connections on top of board and re-soldered any that looked the slighted bit suspect. Is it possible I may have crossed up the wires to the volume pots?

This is my first build, and I feel like I'm so close to having it right, but I'm pretty much out of ideas at the moment.

Any thoughts, suggestions, or places to start checking are greatly appreciated!!

danman
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Re: Need Help! 50w kit

Post by danman » Thu Jul 27, 2017 8:39 pm

First step always is to try new tubes in every slot. Nothing worse than chasing a problem that is nothing more than a bad tube. What are your output tubes biased at? Do you have 1 ohm resistors on pin 8 to measure the idle current? The problem with the channels should be easily found as both channels each use one half of the v1 tube. After the volume pots the signal from both channels are mixed at the 470k resistors where they become a single signal that travels on to v2. If one channel is giving you problems you need to check everything from the 470k mixers back to the input jack. The input jacks are also very easy to wire up wrong so be sure to check them completely. Also make sure that the cathode resistor (820 ohm attached to pin 3 of v1) is properly grounded at one end and the bypass cap (usually 220uf-330uf) is attached properly with the negative end to ground and the positive end towards pin 3. We will need some good, clear photos of everything to be able to help further. You will need to use an image hosting sight to post them though because of the new forum rules.

micahnix1
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Re: Need Help! 50w kit

Post by micahnix1 » Sun Jul 30, 2017 6:53 pm

Thanks danman for the reply. I ended up tinkering with it for about a day after your recommendations. Never could get anything to work, so I completely gutted it and reconnected every wire and component. I have the bias pot pegged and it's running a little cool, about 31-32 mA, looks like I'll have to swap out the bias resistor for a 33k instead of 47k.
Channel 2 is working just fine now, channel 1 is still silent. I can hear a tiny bit of guitar signal with the volume at 0, but when I turn it up, theres a small pop and then nothing. I'm starting to wonder if I dropped a wire clipping or maybe dripped a bit of solder inside that volume 1 pot. Resistance of the pot checks just fine.

Any other ideas or pointers? If I can't get it working I'm thinking about taking it to the local amp guru sometime this week.

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Re: Need Help! 50w kit

Post by danman » Sun Jul 30, 2017 7:25 pm

It may help if you could post some voltage readings of v1. Don't need the AC heater readings at pins 4, 5 and 9 but the DC voltages at 1,6 (plates) and 3,8 cathodes may help. Pins 2,7 are the grids and should not have any DC voltage on them. Other than that we will probably need some pics to help further.

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Re: Need Help! 50w kit

Post by micahnix1 » Sun Jul 30, 2017 8:13 pm

Here's some voltages:

V1 PIN 1: 136v
Pin 3: 1v
Pin 6: 172v
Pin 8: 1.7 v
Snapped some pics. Going to try to upload

micahnix1
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Re: Need Help! 50w kit

Post by micahnix1 » Sun Jul 30, 2017 8:18 pm

Here are some voltages:
PIN 1: 132v
Pin 2: 1v
Pin 6: 173v
Pin 8: 1.7v
Snapped some pics, going to try and upload

micahnix1
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Re: Need Help! 50w kit

Post by micahnix1 » Sun Jul 30, 2017 8:50 pm

Image

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Re: Need Help! 50w kit

Post by micahnix1 » Sun Jul 30, 2017 8:52 pm

Image

danman
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Re: Need Help! 50w kit

Post by danman » Mon Jul 31, 2017 8:30 pm

Nothing appears to out of the ordinary. Voltages are a touch lower than some but that could simply be the PT that you used. What is your plate voltage at pin 3 of the power tubes with the amp properly biased? Either way, the voltage being a little lower should not be giving the problems that you are describing. I would start tracing the connections from the input jack through the 68k resistor pair and then on to pin 2. From pin 2 the signal leaves the plate at pin 6, travels through the coupling cap and then on to the normal channel's volume pot. Make sure the pot is grounded properly! From the volume pot the signal travels to the pair of 470k mixer resistors. This is where the signal is mixed with the bright channel and travels to the grid of v2. We know the problem is in the normal channel so it must be from the 470k back to the input jack for that channel. Check every connection for solid soldering and make sure that you didn't forget a ground connection along the way.

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Re: Need Help! 50w kit

Post by danman » Mon Jul 31, 2017 8:43 pm

I forgot to mention that the 820ohm cathode resistor and bypass cap are also connected to the normal channel. From your readings it would appear that everything is connected properly and that the resistor and capacitor are properly grounded. Just doublecheck that area also.

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Re: Need Help! 50w kit

Post by micahnix1 » Mon Jul 31, 2017 9:00 pm

Thanks again, I'll give everything the once-over just to make sure.
Another thing i wanted to mention: today I tried the chopstick test all across the circuit board, everything was quiet except that coupling cap (I used a .0022uF out of the 70's and up spec board). I can hear a definite pop through the speakers when I tap on it. Could that be my culprit?
Tomorrow I'm going by the amp repair shop in town to see if he has another cap I could try, and to pick up a 33k resistor to swap with my bias resistor.
Also, I've switched out all my tubes with known good ones, to rule those out.
Thanks!

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Re: Need Help! 50w kit

Post by micahnix1 » Tue Aug 01, 2017 5:13 pm

Update:
Replaced my volume 1 .0022uf coupling cap to make sure it wasn't bad, switched 500pf bright cap to a 250pf to rule it out, replaced 500pf mixing cap to 250pf to rule it out.
Went back and re-grounded all my board wires to the bus, made sure both of my 820 resistors and bypass caps had good solder joints.
Channel 1 has a faint signal now. When I turn up the volume I still get the light pop, but instead of completely losing my guitar signal like before, it stays, just never gets any louder. I'm beginning to suspect that one of my white wires may be frayed inside, so that will be the next thing I replace.
Channel 2 still sounds great! :lol:

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Re: Need Help! 50w kit

Post by danman » Tue Aug 01, 2017 6:40 pm

That's a strange problem for sure! Here is another test to try. With the amp turned on and plugged into a speaker cab, standby switch in the normal "play" position and both volumes turned to 3 or 4, probe pin 1 and 6 of the v1 socket with your meter. Ground your

black probe like normal and touch both spots with your red lead's tip. There should be a noticeable pop through the speakers when touching both of these points. This is an old trick to determine if the circuit is passing a signal. Normally you would start at the power tube plates and work your way backwards through the amp listening for a pop. Wherever the pop stops is the stage that is giving you trouble. We know that everything from v2 downward is functioning because the bright channel plays fine, so you only need to try this on v1.

Edit; Be sure to set your meter to DC voltage before probing these points!

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Re: Need Help! 50w kit

Post by micahnix1 » Tue Aug 01, 2017 6:50 pm

I'll remember this trick for future builds for sure! Both 1 and 6 made pops this time though. Does that mean that the problem could be somewhere between my volume pot and the board?
Thanks!

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Re: Need Help! 50w kit

Post by neikeel » Wed Aug 02, 2017 2:49 am

Did you read the reply to your other thread re the V3 voltages?
Neil

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