Amp Issues

[DeadAirMD]

Also, if I want to reflow the solder on the tube sockets, do I need to discharge the capacitors? If so, just the ones in the power supply?

 

[RetiredUnit1]

Just to clarify.....

To run checks on my MM on the test points, I have the amp powered up, on "stand by", ground the MM, and touch to the "Test Point" locations on the schematic?

I did this last night and was getting readings that were lower, but in the ballpark for what the TP's states. A few components (TP4) read OL.

Just want to make sure I'm recording these numbers accurately. I have all the parts, still undecided if I will replace any or take it to a tech. Still want to get some readings so if I go to a tech I have a better explanation to give.

VERY important to stick your UNUSED hand in your belt behind your back. If that hand is touching ground, and you inadvertently touch high voltage with your other hand the current will flow across your heart and stop it or cause defibrillation!!! Be sure someone in the house is with you and knows what you are doing.

Use an alligator clip to secure the ground lead to the ground in the chassis while it is unplugged and caps have been drained, then plug it in and power it up.

 

[RetiredUnit1]

Also, if I want to reflow the solder on the tube sockets, do I need to discharge the capacitors? If so, just the ones in the power supply?

Always discharge the caps, even if you're sure they are discharged.

 

[RetiredUnit1]

VERY important to stick your UNUSED hand in your belt behind your back. If that hand is touching ground, and you inadvertently touch high voltage with your other hand the current will flow across your heart and stop it or cause defibrillation!!! Be sure someone in the house is with you and knows what you are doing.

Use an alligator clip to secure the ground lead to the ground in the chassis while it is unplugged and caps have been drained, then plug it in and power it up.

Oops, two part question. Yeah, just the power caps. Be sure you touch the positive leads of each cap and watch the MM as it drains. So two alligator clips.

 

[RetiredUnit1]

Also, if I want to reflow the solder on the tube sockets, do I need to discharge the capacitors? If so, just the ones in the power supply?

I made my discharge tool out of 10ga wire (I have 1500'), a 22k 5w resistor, heat shrink, a bamboo skewer, and tie wraps. No melted metal when you do it with a resistor. Without it's a very loud pop and the end of your screwdriver is missing.

 

[RetiredUnit1]

These are great additions for the probes when working with high voltage

 

[PunchySunshine]

These are great additions for the probes when working with high voltage

View attachment 67557

 

[Alan W]

These are great additions for the probes when working with high voltage

View attachment 67557

As are these—or you can do a few layers of heat shrink over an existing pset of probes.

 

[RetiredUnit1]

As are these—or you can do a few layers of heat shrink over an existing pset of probes.
View attachment 67562

I like the alligator clips so I can attach the leads, one at a time with one hand behind my back, to the HT and ground so I can watch it discharge.

 

[Alan W]

I like the alligator clips so I can attach the leads, one at a time with one hand behind my back, to the HT and ground so I can watch it discharge.

i use alligator clips also, but if I need to poke around anything with more than ~40 volts running through it, I use probes with insulation until the point, just to keep from hitting things and creating shorts.

 

[DeadAirMD]

Thanks again for all the advice. I'm a big advocate of using alligator clips. I'm going to replace the bypass caps tomorrow as well as some suspect resistors. I've got a discharge pen that worked perfect last time I changed the power caps.

 

[Alan W]

Thanks again for all the advice. I'm a big advocate of using alligator clips. I'm going to replace the bypass caps tomorrow as well as some suspect resistors. I've got a discharge pen that worked perfect last time I changed the power caps.

When you replace the resistors, leave a gap between the board and the resistor body. (I use a popsicle stick as a spacer, then pull it out.) This let’s the resistor dissipate more heat, protecting it and the board.

 

[DeadAirMD]

Absolutely great advice! I've had this amp over 25 years and I've noticed some minor "burning" of the circuit board due to hot components. I'm sure someday I'll get a new amp, but since this was my 1st tube amp I'll have it forever. Have heard way too many stories of artist getting rid of equipment that they later regretted getting rid of.

 

[DeadAirMD]

Well, replaced the rest of the caps today. Did some recording and the audio itself sounds absolutely crystal clear. What an upgrade!

The downside is that the distortion tone still blows. I have some components that are stuck in the mail's limbo lala land, so once those come in it will be interesting to see what those changes bring.

The board was brown,........very brown, under R97 and the two big 5w 470R resistors......