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Post subject: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Sun Jul 21, 2013 5:52 pm
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Yes I know this is an ongoing issue with these style amps.. I have worked on sever Hotrod Deville and Hotrod Deluxe amps in the passed.. Not that im back from Afghanistan my buddies are sending me work.. I have knowledge on the schematics and working on these amps.. But for some reason I can not locate the dang part that is failing! Thinking its in the reverb circuit but its making the sound of frying bacon even when the reverb pot is at its lowest.. Reason I think it's somewhere in that part is because when I play the guitar through the amp on input 1 with reverb pot at 10 it has reverb as its on 3.. When I do the chopstick tap on the spring the reverb is loud and very "surfy" (is that a word?? Lol) please help!!

Pooch


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Sun Jul 21, 2013 6:18 pm
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If the frying bacon sound is present with the reverb turned all the way down or switched off completely, that is not the problem.

Have you swapped tubes? Have you checked the bias of the power tubes? Have you looked at the power tube screen resistors (I have had them fail on mine)? Have you checked for bad solder joints around the tube sockets or elsewhere in the amp? You really don't say what troubleshooting you have done so it is hard to say where to go.

Glad you made it back home safely. :wink: :D

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Sun Jul 21, 2013 7:34 pm
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Thanks!! its good to be home!!
Ok here's what has been done and the values checked just 5 min ago:
First issue was channel switching on its own, so we all know those notorious 470ohm@5w that get hot and pretty self distruct.. Replaced with same value and slapped some high temp RTV between it and the PCB.. Problem with channel switching fixed.
Second issue was the ribbon cable on V1 was replaced with good gauge wire. The ribbon cable was broken off and I don't like reusing the original because it's a pain to work with.
Dressed the wires from the choke, output and input..
Reflowed all solder joints on both PCB's and added solder where needed.
Swapped tubes with another amp and still had the same issue with the bacon frying.
Bias on this amp is fixed but the voltages are as follows (reading pins starting at 12 o'clock moving clockwise):
left output tube pin 3&4=407.3v, pin 5=-43.44v Right output tube pin 3&4=407.3
pin 5=-43.6. Total bias = 43.44v + 43.6v = 87.04v
I replaced the following plate load resistors and their current readings are followed as looking at the back of the amp with the PCB exposed:
R4 top 224v bottom 332v R9 t 208v b 332v R18 t 224v b 332v R52 t 225 b 356.
In looking at the other plate load resistors I saw in the schematic R50 9.1k and R52 91k@1w that I do not have replacements for. Thought of just bridging a 100k across the both of them but the readings on them show R50 t 242v b 253v and R51 t 253v b 366v so I figured there is no real issue there..

C5 was replaced with 250pF@500v silver mica.
C6 was replaced with .1 pF@600v Sprague orange drop.
C7 was replaced with .022@600v Sprague orange drop.

I tried out the clipping of the resistor on the reverb for more control but it sounded to me like it just killed what little reverb the amp already had so I reinstalled the resistor. (Reverb at max sounds like its at 3 on my hotrod deville)

If any of my data showed here is written incorrectly please feel free to correct me and show me the way..

Thanks
Pooch


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Sun Jul 21, 2013 8:28 pm
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Another possibility, re-tension the tube sockets.

http://billmaudio.com/wp/?page_id=171

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Sun Jul 21, 2013 8:49 pm
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Could be an issue.. I have noticed that V1 V2 and V3 are noticeably easy to install. I'll work that issue and get back to you on that one. I've been looking at the schematic more and wonder if coupling caps could play a role in this and how would I check them? What would I be looking for? Think it may be time to buy an oscilloscope.....


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Mon Jul 22, 2013 12:27 am
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Typically, problems with coupling caps will result in hum, not popping and crackling. But, anything is possible. Check them with your meter to make sure that DC is not passing. Check the DC voltage (Plate voltage from the previous stage), on one side of the cap and there should be very little on the other side, maybe a few volts at most.

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Mon Jul 22, 2013 3:35 am
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shimmilou wrote:
Typically, problems with coupling caps will result in hum, .



Hum is a problem with filter caps not coupling

Coupling caps problem is leaking and your hear scratch in pot like some dirt . This is DC voltage passing through.


Last edited by stratele52 on Mon Jul 22, 2013 3:39 am, edited 1 time in total.

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Mon Jul 22, 2013 3:39 am
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Mocheael your problem look to be bad solder as Bluesky write . Check all solder in power supply rail . Also , power tube socket contacts .

Test bias on power tubes . They could be biased too hot or defective.


Last edited by stratele52 on Tue Jul 23, 2013 12:53 am, edited 1 time in total.

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Mon Jul 22, 2013 3:13 pm
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michaelbpuccio wrote:
Bias on this amp is fixed but the voltages are as follows (reading pins starting at 12 o'clock moving clockwise):
left output tube pin 3&4=407.3v, pin 5=-43.44v Right output tube pin 3&4=407.3
pin 5=-43.6. Total bias = 43.44v + 43.6v = 87.04v


These measurements are meaningless. You need to measure the cathode current of each power tube, multiply that value by the plate voltage of each tube and you will come up with the idle power dissipation of each tube. if that value is anywhere between 50% and 70% of the maximum plate dissipation for a 6L6GC (30 watts), your bias setting is OK.

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Tue Jul 23, 2013 1:00 am
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Use Weber Bias calculator ; www.webervst.com/tubes1/calcbias.htm

First line ; stay with " AB class" Tube ; choose 6L6 ( or GC , WGB )

Just enter your plate voltage and click on "Calculate Bias"

Beware ; amp have lethal voltage


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Tue Jul 23, 2013 6:03 am
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stratele52 wrote:
...Hum is a problem with filter caps not coupling...Coupling caps problem is leaking and your hear scratch in pot like some dirt ...


Good description, thanks stratele52. 8)

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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Tue Jul 23, 2013 7:09 am
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michaelbpuccio, I know this is losuy timing, but try this before proceding to major surgery. Get some De-Oxit GN-5 and apply a little to EVERY connection (buss lines, sockets, plugs, tubes, switch contacts. etc). Work the solution in a few times, before firing up the amp. It's worth a try...


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Tue Jul 23, 2013 7:12 am
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Ok I'll be back in the shop today and will get those measurements.. I was doing other things all day yesterday..


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Mon Jul 29, 2013 1:56 pm
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Ok we were all wrong/right.. Lol!! The sound was being made before I made this change.. What I found was the ribbon cable on V1 was pretty bad.. I took it out and replaced the ribbon with good wires... While working at night I saw flashes that came from the PCB where the tubes are attached.. It was arcing even after i replaced the cable with the wires on the PCB where pin 1 and 2 connect to the board for V1.. I used a razor blade to lightly scrape off anything that could be causing arcing between the two points and reflowed the solder... Turned the amp back on and no more bacon!! Another win for the good guys!


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Post subject: Re: USA Blues Deluxe - Popping/Cracking like frying bacon
Posted: Tue Jul 30, 2013 3:52 am
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bluesky636 wrote:
...Have you checked for bad solder joints around the tube sockets or elsewhere in the amp?...


I would say that bluesky636 nailed it right on the head. It wasn't the ribbon cable at all, but cracked solder joints that you saw arcing. :wink:

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