Blues Deluxe reissue failure

[picknconk]

Hi kids,
I bought a BDR off ebay. It worked as it should, ordered the Fromel Mod kit to upgrade the caps, load resistors, etc., but it let go before the kit even arrived. Here's the history....I removed the chassis and tank to replace the speaker with a nice old Fane alnico Blue. I re assembled it, put in 70's American 6L6's without rebiasing( I know, but it won't make it blow up), and turned it on. What I got sounded like a one watt distorted mess. I shut it off immediately, and put the lousy groove Tubes back in. Oh, maybe most importantly, I had lost all reverb function. You can shock the tank, amp, anything,..no 'verb crash. I figure examining the assembly in the 'verb circuit to be the first place to check as I know these amps can have open joints at the blink of an eye, but reverb doesn't usually shut the amp down. So, I turn to you folks for suggestions before I go back in. I won't work on it until I'm not mad any more. I replaced the tank as I have many...nuthin'. I haven't checked the cable for continuity yet, I will, but the output is nearly nothing and a mess at that. How could I blow it up? Check all joints? Sound familiar to any of you experienced techs? I'm bummed big time. The amp looks crispy fresh new, not an old beater. I downloaded the Service Manual for assistance, Tried replacing the pre amp tubes just because,...it's all the same. No pinched wires, no pulled off wires, tank reconnected correctly, alternate speaker check...I'm stumped. Thanks,...Bob

[52 Bill]

Looking at things is helpful when something really cooks, but having some real data will help even more. Look at the pc board that holds the tube sockets. Check all of the tube sockets for cold or broken solder joints.

Do you have a voltmeter? If you do, first check the two low voltage power supplies for + and - 16 vdc. If they are ok, move on to the high voltage section and take readings and compare them to the schematic.

[picknconk]

Will do, but you gotta admit, removing and replacing the chassis shouldn't have broken anything. I've heard endlessly that these need all their joints reflowed, and I am a NASA certified assembler, so my work is good. I will check those voltages, and having the Service specs will make that easier. I wonder if it's a mistake to install the Mod. kit before I find the problem, as it might replace the faulty part. My instincts tell me to fix it first. I also am inclined to replace the supplied upgrade Electrolytics just because. I'll get back to you with any and all discoveries. This forum has helped me with guitar stuff, now it's amp time.

[Mark Black]

Double check to make sure the correct speaker jack is being used. Very easy mistake to make and made even more easy by Fender swapping the location of the main & aux jacks between older & newer models.

Just a thought...

[picknconk]

Did that, thanks. All these op amps and stuff give me the jitters. I'm a point to point, tube guy,..these can be decent, and I got it cheap,...maybe we know why now. Those +-16v readings seem to be at the solid state section..I'll let you know. I'll discharge it, replace the caps, reflow all the crucial joints and start from there. I'm looking for cooties with a new amp like this, the old think doesn't apply beyond the raw basics, of course. I also heard to put Goop(E 6000) or something similar, to ruggedize the sockets. I think that makes sense later...Bob

[g1]

Like you said, much better to fix first, mod later. Just to try to isolate the problem a bit, try plugging in to the "amp in" jack, and see if there is any change in the power coming out of the amp.

[Mark Black]

Use great care when removing the PCB's so as not to flex the ribbon cables any more than absolutely necessary. The conductors are tinned and it's very easy to create breaks where they meet the boards.

[52 Bill]

I suggest as the others here have that you fix first then mod, that way you are sure that a problem is not something that you did. I have no idea as to what your skill set is, but you're right in the fact that just replacing the speaker should not have caused the amp to die.

When you pulled out the chassis, did it get pulled down to the back of the speaker magnet? A simple jolt like that can cause a loose connection to open up entirely. The fact that the reverb is completely dead would also point to a low voltage power supply problem, as it is entirely based on the op amps.

Even though there are no op amps in the signal chain unless you use the break jacks, there is an fet that needs to be powered by the low voltage power supply in order to turn it off and not mute the signal going into the power amp.

[Enzo]

My consistent advice for these is to look CLOSELY at the solder on the power tube socket pins for small cracks. I usually just resolder them all anyway. Then verify B+ on BOTH pins 3 and 4 of all power tube sockets, AND look at pins 1 and 6 of the phase inverter for missing B+. And verify reasonable bias voltage on both pin 5's.

You didn;t bias it? Well, that takes 20 seconds, so do it. No, having the bias off won;t blow up the amp, but if the bias reading at the test point is way off, it can be a clue as to what is happening, or conversely if dead on it can tell us the output stage is healthy.

Get the "how could I have blown it up?" thoughts out of your head. pretend someone just dropped the amp off this way. We don;t need preconceived notions getting in the way. WHo says you blew anything up? It could merely be a coincidence it failed now. Or even if you did something, it might more likely be a wire that broke off in a ribbon than anything blown up.

We mentioned the wrong speaker jack. If you plug into the extension jack, the main jack will still be shorting across the output. result very low and distorted output. However, the signal for that main jack comes THROUGH the switching contacts of the extension jack. SO clean and verify the contacts in that other jack.

And failing that, pull the output transformer secondary wires off the jacks and clip wire them to a speaker. A failed jack can short itself out.


But having said all that, here is my other suspect. The two JFETs that mute the circuits. Look at Q1 over by the power amp jack on the print. If it is leaky/shorted or stuck on, you get little signal through. Q2 mutes the reverb similarly. JFETS are ON until turned off by voltage at their gates. If that voltage is missing, they never turjn off. And since these JFETs go from signal path to ground, that is a signal killer.

Right in the center of the drawing is teh mute circuit, TP30. What is happeneing there? That control signal is coming from all those op amp-y channel switching circuits, and what do you know, they need the +/-15v supplies.

[picknconk]

I'm not finding any bias info. Can you give me a measurement to shoot for? TP location on the print? I'm so old fashioned, this thing is intimidating me. I haven't been back to it since my last post...stuff going on, and plan to flow all the joints as they look really poor to me and I've heard they are. Jfets are Indian territory to me, I will look at the print( I can read prints) and locate this stuff. Teh Mute? I'm clueless. I'll find TP-30. Will check voltage.
So...help with bias set
Drain amp
fix solder connections.
take low and high voltage measurements and report back...thanks...Bob And check jack condition How about removing the extension jack from the circuit, I don't use them..?It just looks parallel to me. No? You said it passes through the extension jack..
Any additional basic info on Q-1 and Q-2 is what I need. I do not know the function of these things, I am pure tube and old tube amps at that. I don't understand the muting function, but can take a reading at a point given instructions. JFET stuck on....?Dunno. I hope it's a physical break, as that I can find and fix. If it's in a solid state gizmo, I'll have to turn it over to somebody. I am an assembler, aero space level, and can follow instructions, but will never claim to be a tech. I could have bonked it removing it, and the Fed Ex guy was a gorilla, but it worked before I swapped out the speaker. My hope is chintzy workmanship. The ground lead alone looks barely connected, so I start with that. Brittle ribbon connections? Got it...Bob

[52 Bill]

I'm not finding any bias info. Can you give me a measurement to shoot for? TP location on the print?

The bias test point on the schematic is TP26, it is between the two output tubes. You set the idle bias by reading the dc voltage from TP26 referenced to ground. Set the trimmer so you get a 60mVdc reading. On the actual amp, this test point is located at the far left end of the tube socket board.

Jfets are Indian territory to me, I will look at the print( I can read prints) and locate this stuff. Teh Mute?

Q1 is the mute for the preamp output, it works like a switch by grounding out the signal before it goes to the power amp. If it is shorted or is not being turned off there will be no signal going into the power amp. If you have the service manual pdf, then there will be a page with a pictorial layout of the pc board. This pictorial is marked with the location of all of the parts and the test points as well.

And check jack condition How about removing the extension jack from the circuit, I don't use them..?It just looks parallel to me. No? You said it passes through the extension jack..

Don't get ahead of yourself here. There are a lot of facts being thrown at you all at the same time. While any of these things can cause your symptoms, you should start with the basic stuff first before you start thinking about curing non-existent problems.

[picknconk]

I'm beginning to get the drift. This solid state muting function is all new for me. I'll follow your advice(all of you, thank you very much), and proceed with data as I gather it. You folks are being so instructive, I may pull this off! Give me a 6SJ7, a 5Y3 and a couple of 6v6's and I'm good. This thing is quite a different beast. I'll laugh if it's a broken joint after all, but learning is always good. Thanks again, ...Bob

[picknconk]

O.K., I haven't gone away, or taken the amp to a shop( no dough anyway), I've been researching all this stuff I do not know and reading the factory service Manual that I downloaded. I now have a moron's block diagram grasp of the effects loop switching, and some of these components as they apply to the amp. I'll flow all joints, fire it up, set the bias to rule out the output stage, try installing something in the loop, check for change in function, remove if nothing, report if something, take all TP readings you told me to and let's see what we've got. I build Analogman Bi-Comps piece work for a living, so I'm busy a lot. Aero space quality pedals...Bob
HEY EVERYBODY!...Is there any good reason why I shouldn't replace those dreadful ribbon cables with individual wire? I hate them, they're too rigid, and I want to shorten the lead length. Their stiffness and mashed down configuration lend themselves to problems....any responses? Thanks...

[Mark Black]

On the ribbon cables: Replacing them with individual wires MAY lead to unintended consequences. I had issues with oscillation after trying that in an amp of that style (don't remember the exact model, but one of the Fender Blues/Hot-Rod types). I think the parallel & equal length wires of the ribbons are part of the overall finished product design.

On the other hand that particular amp may have just been more prone to oscillation. Be interesting to see if others here have done that wire replace with better results.

[picknconk]

Thanks for the input. May I ask...did you use stranded wire? Solid wire is the only thing to use in signal path wire. I see the ribbon wires are solid. I was just looking to reduce the combined flex force of the ribbon, plus shortening the wire. Maybe slicing the sections in between the conduits plus shortening is all I need to do. What do you think of that idea?...Bob Stranded wire will lend itself to oscillation. The old cloth solid radio wire is still some of the best stuff for what we do. I never pass up the chance to cannibalize an old chassis, but the days of finding them is all but over. I won't be using the Drive high gain function, which is where a lot of the fun starts with these things. I wanted a clean, loud cheap amp. As soon as I get it working again.