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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Thu Jan 02, 2014 11:14 am
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You may want to consider a nice, heavy duty AC power conditioner --- if your AC power is that succeptible to surges. And the amp is that sensitive to these AC line irregularities and lightning strikes.

Get a good one, if you want piece-of-mind protection. A lot of lower end multi-strips appear to all be made with questionable Chinese components. I have heard & read about many of these products worsening the AC noise. And not being able to protect themselves from AC spikes, let alone a tube guitar amp.

Personally, I feel that the well-designed PSU of most Fender amps is way better than most aftermarket multi-strip products. However, for truly clean AC for tube amp usage, resistant to surges --- the Topaz Ultra-isolators are the best things. AKA "the ultimate boat anchor" with +100dB down filtering. Imagine a PT with this kinda iron! :lol: :lol:


Good Furman Strip:

http://www.amazon.com/Furman-Advanced-C ... onditioner


"small" 0.5kVa Topaz:

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Thu Jan 02, 2014 11:54 am
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Posts: 16
WARNING very long post.
a long summary - read only if you interested.

After all the posts, I felt I need to clarify a few things.
In my very first post I mentioned the things i did before asking for help.

On Dec 21 I wrote:
I am comfortable working on amps and discharge capacitors each time before digging in.
Been using homemade audio probe. Recently bought an oscillocope and audio generator, need to learn to use.
I have a schematic for this amp.


Here is a list of what I have tried and what I have done.

1. Installed new f&t filter caps and have a new set of jj tubes.
2. Replaced plastic input jacks with switchcraft.
3. Repaired broken traces and lifted eyelets
4. Checked all resistors and replaced any open or out of spec with schematic
5. Power amp in produces sound so I assume problem is in preamp section
6. No sound from preamp out
7. Checked tube pin voltages and will post them tomorrow
Can someone post what all pin voltages should be for v1 v2 and phase inverter

8. Tried to use fender test points, but can't get millivolts AC to read on multimeter.
9. Yes I have speaker plugged into correct jack
10. I have traced audio through r20 then it stops. R20 tests good. Continuity is good to r22 but no audio there.


Before posting at all.
Put in new tubes.
I considered it a logical and quick approach to locate any resistors
that were bad. I did this and replaced about 6 resistors.
I visually inspected the board for any lifted or broken traces.
I found some and fixed them.
Input jacks were a nightmare. someone prevoiusly had tried to fix broken trace mess on back from jack movement. I had to fix it right with switchcraft jacks and leads taking any physical movement of the jack out of play in destroying board solder joints.
20 year old Illinois, so replaced with F&Ts.
Tried to measure all test points , but my flike 77 will only read down to 600mVAC.
Then started tracing audio with homemade probe. (this has always been a good tool. along with a mulimeter I have fixed several of my older point-to-point amps)
Traced audio through R20.

It was suggested that I post pin voltages, which I did.
It was suggested that I post heater voltages, which I did.
All voltages were good.

stratele wrote: All voltage look good , signal path may be broken or short

The next day Dec 22, One day after the first post I (fretworks) wrote:
Suspects in the direct circuit appear to be r21 master volume which checks OK.
Ry2b which appears to work as it should. How do I further test this?
Power amp in jack. How do I test this?
Q1 how do I test, and can this be removed to see if is the problem?
I am here today working hard on this all day
Thanks again for your help and ideas, I will check through them all.
I am going to drop the top board down again and look at the rear trace from r20 to r22
I am a little worried about the fragilness of the ribbon cables. I have already repaired one lifted trace there.


Had I known, at this point in time, how to test Q1 or that it would be ok to remove to see if it was the problem, this thread would be a lot shorter. I also expressed at this point fear of the ribbon cables (which ultimately were part of the compound problem.)

I should have followed stratele52 advise to remove q1. Instead, I got caught up in trying to follow the other advise of stratele52 and jumper around from r20 to c14.
there was simply not enough lead to do this with board in, and with board out (results were being effected by the ribbon cable intermittent faults).
I went ahead and checked power in jack by removing and using schematic to test operation. It tested good, and was a good learning experience reading the schematic and applying to the jack for test.

I should note there that there have been quite a few posts discouraging my approach or my removing components unnecessarily. I understand, as most hobbyists are probably not as focused and obsessed with profection when it comes to soldering.
I have been soldering since I was a teenager (I am now ancient). I already mentioned that I fixed quite a few broken and lifted traces.
I use the appropriate low watt 15 and 25 pencil tip irons with silver solder and flux.
I clean all flux afterward with 91% isopropal alcohol. I desolder with braid and flux as to not lift traces. my solder joints are always secure and shiny. Afterwards, I test both sides for continuity of circuit. Basically, after I solder, it is good to go.

When I asked: I have confirmed continuity to ground after r20, so am I right to be certain that something is shorting or opened to ground?.....
bluesky636 confirmed with this: Q1 functions as a muting circuit when switching between normal and drive channel. When switched, the signal path is momentarily shorted to ground. If you are measuring a short from the output of R20 to ground, Q1 is either shorted or there is a problem in its power supply that is keeping it active.

After this, that evening I had it solved at q1. But other problems, detailed in my post just after midnight kept me from knowing for sure. Ribbon cable and speaker jack, both problematic and intermittent. Cable, based on what postion the board was in, buttoned up or laying out flat for access to rear of board. and jack based on volume and vibration causing loss of contact or touching shunt.

I wrote: Removed q1 with no change. Then I dropped the board down again and thought I would probe for audio at c 14 back side, but before I started probing , I finally had sound - and very loud at that.
So now I am thinking I missed something with board up, and maybe q1 was the problem after all.

I also mis-posted that I was testing cr22 and cr23, I just typed this wrong. I should have read cr2 and cr3, as these are in the relavent circuit. I can see where this might have raised some eyebrows, and caused someone to think I was jumping around.

Also, seems things took a bit of a negative turn when I posted:
Whatshould I concentrate on next? Ribbon cable ?
What is anyone's take on replacing those ribbon cables with individual wire?
Am I guessing in the right direction? Seems to me that if it were components, they would not cause the popping when i barely move the board. Seems like stress on the fragile cables or connections at the board. I will look for lifted traces there.
Any other ideas?


I never should have written "am I guessing in the right direction" It should have been put more like, In anyones experience, what should I do next. On my own I went ahead and found my suspicions were right about the ribbon cable.
I wrote:
First. I Was right about the fragile ribbon cable. I started the day by doing a really good visual check with a magnifyer and light. Sure enough, first ribbon cable to top board from v1was a mess and had lifted traces and poor connections. I know now that this was my source of confusion yesterday, creating the popping and letting the amp function when board was in down position. Someone had been in this amp before me, and had this cable off. I de-soldered and stripped back ribbon cable about a half inch. Cleaned up the area of old solder and flux with alcohol. Used an exacto knife to scrape along trace to expose copper. Slightly less than a half inch. I did this for all six. Pushed wires through holes and up tight, bent them over against board and lined up with traces. Soldered the wire down along the trace so I now have a good long connection. This worked out well and is a really good firm connection now.

Well this should have fixed eveything, but NO, now I encountered the speaker jack problem.
I wrote:
Fired the amp up and she sounds great with no problems. But wait, about 5 minutes into playing , sound dramatically and suddenly drops to very low and distorted. Not like what we started with, but a bit louder than that , but horrible distorted sound. I was really crushed and thought now what? Have I burned a resistor or other component?

I was about to shut it off when i thought to check for anything with the wooden dowel. Surprise. When I pushed on the speaker jack, sound came back full. I bent the jack connections in a bit so that when a plug is inserted the shunt is a bit further away from signal arm. Yet still closes well when plug is out. I also gave it a good cleaning with contact cleaner.


Q1 took care of the surge in volume just after turning off the amp.

bluesky636 wrote: As I described earlier, Q1 is part of the muting circuit to prevent pops when switching between the clean and drive channel.

he did not mention that this would cause the volume surge at turning off amp.
I rechecked all bleeders and they were fine. So was Q1 responsible for this as well?

As I already mentioned replacement Q1 jfet111 is in and amp is 100% and I am very happy.
At no point did I feel like I was over my head. Even if I was, I learned alot. I acquired the amp dead, and figured I don't have a lot to lose. It was a great educational experience.
Thanks to eveyone who posted with help


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Thu Jan 02, 2014 11:58 am
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Joined: Sat Dec 21, 2013 9:36 pm
Posts: 16
BMW2002Ti wrote:
You may want to consider a nice, heavy duty AC power conditioner --- if your AC power is that succeptible to surges. And the amp is that sensitive to these AC line irregularities and lightning strikes.

Thanks, my power is fine, this happened with previous owner.
I suspect this is rare, and that these amps are not typically that suseptable.
Anyone with a blues deville ever had this happen?


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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Thu Jan 02, 2014 2:58 pm
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
fretworks wrote:
Q1 took care of the surge in volume just after turning off the amp.

bluesky636 wrote: As I described earlier, Q1 is part of the muting circuit to prevent pops when switching between the clean and drive channel.

he did not mention that this would cause the volume surge at turning off amp.
I rechecked all bleeders and they were fine. So was Q1 responsible for this as well?


I have no idea why Q1 would cause a surge in volume. :?

Glad you have everything fixed. :D

This thread illustrates very clearly why it can be difficult to diagnose amp problems over the Internet. :wink:

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Post subject: Re: 1993 blues deville 2 x12 low to no volume i need help
Posted: Thu Jan 02, 2014 3:23 pm
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bluesky636 wrote:
...This thread illustrates very clearly why it can be difficult to diagnose amp problems over the Internet. :wink:


+1!

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

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