Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on May 20, 2012, 11:44:43 am
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I have a Fender HotRod Deluxe that motorboats badly when engaing the OD channel. The master still acts as a volume for this channel but the Drive pot is acting like a tremelo speed pot. As the Drive pot is turned CW the motorboating increases in speed. The clean channel volume is slightly still present at CCW position even after the OD channel is disengaged. I dont belive it is relay related. But i have ordered 2 new relays just the same to have if needed. What in the schematic could be causing this? Im looking at diodes and transistors now
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It's hard to believe this was ever stable. Four cascaded stages on one power decoupling cap, sheesh.
Replace C36. Be generous. 100uFd may not be too much.
A better design: lift the higher-voltage ends of R4 R11 out of the PCB. Solder them together with a 10K to the + end of C36 and a 22uFd to the - end of C36.
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C36 was the problem alright PRR. Someone recapped the amp with some real cheesy caps.
The last one i took out was blown out. Now to tackle the More Drive switch which quit working.
Channel switching is working fine. Cant thank you enough PRR* :worthy1:
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The more drive switch goes through the LED.Usually resoldering the contacts will do it.Follow continuity on the traces with your meter.
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The more drive switch goes through the LED.Usually resoldering the contacts will do it.Follow continuity on the traces with your meter.
Great. I'll have that amp back on the bench later today and see what happens after resoldering. Thanks.
By the way, your name should be my name! phsyconoodler / I think Steve would agree! LOL!
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Traced and resoldered all points of more switch. No Mo action. Checked all diodes except for CR16. I cant find CR16 on the board. D16 to me. It should be near Q1 & Q2 but it is hiding and not in my veiw. D19 is next to it but i can see where that is on the schematic and not directly linked to Q1 & Q2
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C36 was the problem alright PRR. Someone recapped the amp with some real cheesy caps.
The last one i took out was blown out.
OK, yes but to me is why did they have to replace the B+ filter caps in an amp that's, what 4, 5 years old?
Brad :think1:
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> I cant find CR16 on the board. D16 to me.
CR = Crystal Rectifier, an old-old name from the days when a non-vacuum rectifier was magic.
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D16 is MIA PRR and not next to C44 or Q1 or Q2. Is there another schematic for a later model Fender Hot Rod Deluxe? Have i completely lost my mind? (dont answer that)
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Perhaps the diode was redesigned as R106.
Why are you suspecting the diode? Monitor TP36 MORE_DRV, it should go -14V to +14V. The FET Gates (the pin not traced to R23 R24) and C44 should go way negative and a half-Volt positive. Does it?
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TP36 is showing -16VDC. The FET gates are both showing -7.75. There is no + voltage when engaing the More switch. Im calling it the smore switch
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The more drive switch goes through the LED.Usually resoldering the contacts will do it.Follow continuity on the traces with your meter.
If the red LED is bad would this make the More channel not work? Is that possible?
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Yes.
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I still have no (More Drive) switching. Replaced Q1 & Q2 J111. More red LED will light up if i engage the OD & More switches before i turn the amp on. When i release the more switch it goes off but will not come back on like it should. Could this be related to the footswitch circuit? I plugged in the footswitch 2 weeks ago and this is when i lost the more drive function
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Yes,the footswitch jack itself will cause you grief if it's wonky.It will do all the tings you are describing.
I have had two HRD's with sprung footswitch jacks.
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Yes,the footswitch jack itself will cause you grief if it's wonky.It will do all the tings you are describing.
I have had two HRD's with sprung footswitch jacks.
I put a new footswitch jack in it but still the same. This is a very akward issue. The damdest thing it works if i engaging the (M)switch before turning the amp on. I was think a capacitor is bad. This one is kicking me
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I found the problem with the (more) switching and put together the following chain of events
When the amp first came in i put 2 new relays (K1) & (K2) on the board because i had a problem with still having volume on the clean channel along with the OD channel engaed after the pot was full CCW
That solved the clean channels problem. Then i plugged in the footswitch and the more channel dissapeared
Then i replaced the footswitch jack as it was bad and not connecting on the ground side
Finally i went back to the K2 relay i had installed earlier and replaced it with another one
More channel is back and working fine. I assume that i killed the new relay because the footswitch jack was bad and must have spiked the new (K1) relay
I had no idea the footswitch jack was bad or would harm the new relay
What a long lesson and PITA
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Bet the relay was junk.Never heard of a bad jack harming a relay.
Lesson learned:new does not always mean good.
Glad you got it fixed!
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Thanks for all your help phsyconoodler. Im glad i found it too. It was driving me mad. I wish i had a hydraulic press. I want to squish this relay thin as a piece of paper