Hum problems from a Hot Rod deluxe

[bsco]

the older amp uses a jack type that has staggared pins. The newer unit has a jack that has the solder pins located at the four corners of the bottom of the jack. (mono)... so these must be the newer style you are referring to...they are soldered in place and flat to the board so they must be correct. Actually I was beginning to think I should take a look at the traces, but because the guitar played ok, I shrugged it off so to speak. And if I turn down the clean volume control, the hum turns down...so the problem has got to be before the volume control...... the tube has been replaced and voltages measured,components checked,.so the only thing left really are those jacks.........and it also happens to the drive channel. That volume control will also turn down the hum... Good idea.....I will have another peek tomorrow and post what happens....
Thanks..........

[Jazz P Bass]

Hot-Rod DeVille | Input Jack
Excellent web page.

[bsco]

Thanks for the link. The jacks that are in this Hod Rod Deluxe are the newer type...I'll have to take a look today and post my findings....

[Yelly]

As Jazz P Bass mentioned, you should measure DC voltages after the coupling caps too.
But, I do not think this is the problem. First, I would narrow down the problem:
You say that the hum disappears when you turn the Volume down. So the problem likely is just around this pot or anything before that.
Since the problem also appears at the Drive channel, problem is unlikely the coupling caps C18 and C23, for they should both be leaking DC then.
Are you positive, that V1 is ok? Try grounding directly at pin 2, what happens? Try pulling V1 out, what happens?
Since both Drive and Clean signalpath goes through K1 Relay, have you checked this relay? If you don't know what to do, pull it, turn drive to 0, jumper wire wiper on Volume to joint R41/R44 and try the amp on clean, is the hum still there?

You have to isolate more instead of changing components everywhere.

all the best

[bsco]

Thanks Yelly for the advice. I have had the flu for the last week but I am feeling much better now. I'll check out you're suggestions and post what I find. Once again...thanks for the help.

[bsco]

I pulled V1 out as you suggested and the hum that was originally there went away but another non adjustable hum appeared which was like a buzzing sound that cycled on and off. It also occured with the drive channel activated as well. When I put V1 back this buzzing hum was still there. I then changed the 3 12ax7a tubes around and this hum went away...don't know what caused it...now I am back to the original porblem..These tubes are all new....When you mentioned to ground pin2 of V1 did you mean to ground it directly or through a low value resistor?

[Jazz P Bass]

When you mentioned to ground pin2 of V1 did you mean to ground it directly or through a low value resistor?

You can use a resistor, a capacitor or a straight shot to ground.
Neither one will "kill" the circuit.
But each one can help to shed light, in a specific fashion, on the problem.

[bsco]

OK. Thanks. I'll try that shortly and let you know what I find. I am beginning to wonder if some of the low level hum I am also hearing might be due to the fact tht the chassis is removed from the amp...never the less the problem I am having at the moment is definately not right....I will get back to you as soon as I try this.....Thank you very much...

[bsco]

JUst grounded Pin2 if V1 through a 1 ohm 2 watt resistor and no change. Grounded the other grid, Pin7 of V1 and the hum stopped. So I have a problem between theese two points. Note that when I grounded Pin 7 of V1 and activated the drive channel I got a buzz inthe speaker...I might have two problems so I will tackle he first one..adjustable hum with the clean volume control. Maybe once I find the cause of that, this other problem will dissapear also. I'll keep you posted.

[bsco]

I did as you suggested and when Pin2 of V1 is grounded, no change...however, when Pin7 of V1 is grounded, the amp is quiet. So I have a problem in that area. Upon further very close inspection, I discovered that a solder pad was broken away from the circuit trace but you would never know it by looking and when a meter lead was placed there to check for trace continunity, the pressure would make the pad contact the trace. I am going to give all pads and traces in that area a very close inspection and temporarily install the board back into the chassis to see what the end result is like. I'll let you know how it turns out. Thank you, thank you very much for pushing me in the right direction.

[bsco]

Just put the chassis back in and guess what...the hum is still there. I believe that this is the Hod Rod Deluxe from Hell...
Oh well...back to the drawing board.

[g1]

The hum is still there whether in clean or drive mode? When in drive you can kill the hum with the drive pot and likewise with the volume pot in clean mode?
Grounding V1 pin7 kills the hum, so that doesn't leave much except the relay, R41, or R44. Make sure the one end of R44 is grounded. Check R41 & R44, resolder them and the relay, check for any DC on V1 pin7.
Did you try what Yelly suggested as far as removing the relay and using a jumper?

[bsco]

The hum is still there in both clean and drive. but it is much more noticeable when in drive mode. Also, when the drive mode is activated, and the drive control turned all the way down, if you turn up the master volume you get a buzzing sound in the speaker...if you then turn up the drive control, the buzzing is louder and then you also get the hum that is coming from the clean channel as well. When in clean mode, you can kill the hum by turning down the clean volume control. When in drive mode you can do the same thing by turning down the drive and master. Note that the hum in the drive mode is more buzzy than in clean mode. I haven't tried removing the relay yet, especially when I found that bad solder pad. Grounding pin7 of V1 will kill the hum in the clean channel but not the hum in the drive channel. You have to ground pin2 of V2 in order to kill the nasty buzzing hum in the drive channel. I am going to check the connections to all the associated components between these two points. If that don't solve the problem I'll pull the relay and try what Yelly suggested. Any other suggestions greatly appreciated. Thankyou very much for your time and advice....

[g1]

Grounding V1 pin7 kills the hum, so that doesn't leave much except the relay, R41, or R44. Make sure the one end of R44 is grounded. Check R41 & R44, resolder them and the relay, check for any DC on V1 pin7.

My apologies, had a brain fade and that statement is incorrect. Grounding V1 pin2 did not solve the hum, but shows that the jacks etc. should be ok. The problem should be between V1A pin2 and the volume control. I'm not concerned with the drive setting right now because you will always get more hum/buzz with the drive setting.

[bsco]

Thanks for your advice. I checked all the associated components and they were fine. Checked trace continunity as well. Then I started to check anything associated with the word drive...found a capacitor...C48 I believe...it is tied to the drive switch. anyway replaced that and the hum dissapeared. Also found out what was causing the irritating buzz in the drive channel as well. Apparently, the amp was picking up interference from the lighting over my bench. I am running three 40W incandesent light bulbs overhead....When I reassembled the amp the clean channel was super quiet but the nasty buzzing remained. When I took the amp off my bench and laid it on the floor, the buzz went away...I thought that dimmers and floresent lights caused this sort of thing...guess I was fooled. Anyway, I am a very happy camper right about now. I have left the amp on for awhile to give it a good burn in just to make sure there are no other issues. I want to thank everybody for their input and advice...I don't think I could have repaired this amp without it. One thing is for certain..I won't forget this problem any time soon...
Cheers.