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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Aug 22, 2012 2:46 am
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Yeah Vintage, I'm a neantheral with computers. My bad!!! The 768 should be the one(thanks Beemer). You know this was the first redesign, by the CBS engineers. Or rather a first design for this amp. You will have to go through the bias section components very carefully! The lose of vacuum in a power tube is pretty rare. At this point, I would not invest in a variac, unless you intend to do quite a bit of amp repair work. But you can build a simple current limiter. The guys can direct you to the appropriate site. Oh yeah,"PT"= power transformer. Art

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Aug 22, 2012 10:07 am
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BMW2002Ti wrote:
To find correct OEM circuit, prolly best to pull amp from cab and inspected layout:

http://vintagefenderamprepair.com/wp-co ... Layout.pdf

and schematic (of the AB768 BMR):

http://vintagefenderamprepair.com/wp-co ... ematic.pdf

Some nice detailed photos of your amp under the hood. Of the wiring ----be still my pounding heart, sorry it's kinda peccadillo I have for these older amp layouts --- would really help narrow down the specific circuit type.


I was running through my collection of schematic PDF's to see what I had and I ran across this one that a Amp Tech I had used a couple decades ago from LA had given me
after he serviced my amp. I looked at the BMR again and realized mine is actually a TFL5005D model. So I'm thinking I actually have a AA1069 circuit. Isn't that similar to the silver face Showman or Dual Showman models? I thought those were TFL models too.

Opps, can't upload a pdf, so here is the same AA1069 schematic on a website:
http://www.freeinfosociety.com/electronics/schemview.php?id=852

Any of you guys familiar with this circuit as compared to the famed AB768 circuit?


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Aug 22, 2012 7:26 pm
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To see if there was some hybrid work done between your circuit and the other OFM ones posted by Fender. You should pull the amp out of the cab. Drain the main caps. Take some photo of chassis and tranny side. Try to get stamped data on the transformers & potientometers,

More visual data, the better, Post onto, say PhotoBucket. Then , copy and paste specific items. This will help narrow down bad components, mods, leaking lytic, grounding schemes. Good photos are almost as nice as bing there on the bench.


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Wed Aug 22, 2012 8:00 pm
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Yeah Man, the 768 and 1069 are different animals, bias wise. The TLF5005D is a generic designation. More of a model code, not the specific circuit. The Showman was TLF50005D. Like Beemer said, You'll have to determine the actual date. Or else just scope-out the bias section and compare it to the schemos. HTH, Art

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Fri Aug 24, 2012 10:51 pm
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BMW - I got the chassis out of the head late today after a long day at the studio and did some inspection and pics. Soon as I edit the pics I will post for yall to play Dr. House on. On first blush inspection, I'm seeing some light possible leakage from the caps on the circuit side over the preamp section. But when I pulled the cover off the big caps, nothing - clean. Have not taken a close look at resistors or small components.

Art - talking about the TFL5005D designation, what the hey it means and the correct amp circuit; I thought I'd look for more info, possibly doubting that mine is a 68 and actually a 69. Well I ran into another forum called The Steel Guitar Forum http://bb.steelguitarforum.com/viewtopic.php?t=223160&sid=e2c08be9cdaa5ce9d705f37e55786937 where I read the most ridiculous explanation of the TFL designation .... I think, sorta and I think some wrong info too.

I'm leaving it up to you experts to refute or verify, even partially, this thread info. The topic OP was referring to a Dual Showman and BMR TFL models, claimed they had "Circuit: AC568, AA768" which know is wrong from too many other sites that say neither circuit was used from 1968 on, it was then the aa1069 at least for the BMR. True?

Then another guy's post claimed that TFL stood for Teflon, as was used as wire coating, and that TFL meant: "I just read that the 5000 in TFL5000D stands for the DuPont/3M (Teflon) Part Number" :roll: :lol:

Well a problem there is, then why did the BMR have a TFL5005 number and the Showman a TFL5000 number?? I seriously doubt that they used two different DuPont Teflons (2 diff part numbers of Teflon) for two amps that are essentially the same except double the wattage?! Does his explanation sound as nuts as I think it does?

Question: What's the best way to discharge the big caps? And, know of any good tutorials on how to correctly bias tubes on this BMR and any Fender amp? (I've got a 65 Super Reverb that is screaming (weak) for new Power Tubes and also my 66 Champ)


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 1:01 am
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Vintage, can't argue with the teflon designation. Just don't know. But TLF numbers, on the site are inline. It's still a matter of finding out whether your amp is a 768 or 1069. We would then have a better handle on this. A method to discharge the filter caps: An 18 AWG jumper cable with a 470ohm 2watt resistor in-line with alligator clips at each end; can be attached to pin #1 of V1 and the other end attatched to the chassis for a minute or so; then attach the clip to pin# 3 of a power tube. An alternative is to open -up the filter cap housing and discharge each cap. Then check the residual DC voltage at these points. Be warned!!! Filter caps have a memory capability, and can re charge. So it's not a bad idea to leave the discharge jumper connected while you're in the amp. Actually think, Beemer or Stratele52 might have better info!!! Art

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 1:32 am
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stratele52 wrote:
Your 's 6L6's could be short.

I first do a test , removing those 6L6 , put a new fuse and try if it blow and if GZ34 arcing.

If no , put new 6L6's and adjuts bias

If yes, do some test as Aclemmpoppi , Retroverbial and BMW suggest



Vintageguitarz,
Why don't you begin by this simple and easy test ? Most of the time this is the problem ; 6L6's.

After that if you want to rebuilt your amp with fiters caps ect it up to you.


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 7:09 am
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I agree stratele52

The tube glass was broken some time during the short period of storage, not broken because of some bad components in the amp. The broken tube is the cause of the problem, not the symptom.

The caps in the amp didn't go bad after only a few months of inactivity, and caps didn't cause the output tube to break. The OP said that the caps were changed not that long ago, not original caps.

KISS :wink:

JMOOC

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 12:23 pm
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6L6's could be short inside .


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 4:29 pm
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shimmilou wrote:
I agree stratele52

The tube glass was broken some time during the short period of storage, not broken because of some bad components in the amp. The broken tube is the cause of the problem, not the symptom.

The caps in the amp didn't go bad after only a few months of inactivity, and caps didn't cause the output tube to break. The OP said that the caps were changed not that long ago, not original caps.
JMOOC

Guys, let me clear something up first, I do seriously believe that the Power Tube that went south and cracked was a immediate result of that day that I was demo'ing the amp, not cracked as a result of during the storage period, like mishandled. Last time I showed the amp at the studio (about 4 months ago) it was fine and sounded pretty damn good (though be low on power). I turned it off, waited about 30 minutes for it to cool down and put it back in the locked equipment room. Hadn't been touched since. Now I didn't hear anything pop or crack when I powered up, so I can't say for sure that it didn't crack while cooling down and I was out of the room. That tube also had white powder on the top of the tube (hanging upside down) and white residue "splattered" against the side of the tube across from what I think is the cathode?

stratele52 - Before I try your suggestion, I'd love it if it's this simple, I'd prefer all you experts have a look at the pictures of the chassis and components, I took. As the closeup of the two Caps on the preamp side of the circuit show, I believe they are leaking some Electrolytic. Yes? The Main Cap under the can look fine to me, I think these are the ones the Amp Tech up in LA / Hollywood changed out with NOS original ones the last time I had it serviced about 15 years ago. (It was my stage amp and I stopped using it about 11 years ago)

Here is a link to the PhotoBucket album with all the detailed chassis pictures, just click on the thumbs for the full size picture. Maybe you can use some the Chassis Stamps and Transformer dates to decide if this is a 68 or a 69 BMR TFL5005D? And which Circuit this is: AA1069 or AB768 (or worse a AB568). http://photobucket.com/BMR-TFL5005D

Here is a couple pics, one of the suspect Leaky Caps on the circuit side (preamp?) and a couple over-all Chassis pics top and bottom.

Image
Leaky Caps?

Image
Chassis Circuit Side - Note Date Stamps and 2 possible leaking caps

Image
Chassis under side. - Note Chassis Stamp top right corner


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 4:37 pm
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The output-stage architecture seems consistent for the AA768 revision. The chassis itself was completed in the 43rd week of '68.

Arjay

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 5:44 pm
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Retroverbial wrote:
The output-stage architecture seems consistent for the AA768 revision. The chassis itself was completed in the 43rd week of '68.
Arjay


Thanks Retro, relieved to find that it's a '68 after all. From what I'm reading the AA1069 didn't start until 69 or 70? Do you think there is any other way to confirm which circuit it is other than tracing the schematic to each and every component?

What do ya think of those leaky Caps? Bad?


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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 5:48 pm
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It does appear to be an AA768:

http://vintagefenderamprepair.com/wp-co ... ematic.pdf

http://vintagefenderamprepair.com/wp-co ... Layout.pdf

The 25/25 caps are for the preamp and reverb/tremolo tubes. I would definitely replace them. Once those are replaced, I would again recommend pulling all tubes (except the rectifier, of course) and checking the supply voltages. Then you could plug in the preamp/reverb/trem/PI tubes and check the voltages again. Finally, install the power tubes.

You might want to consider replacing the power supply caps as they all appear original. They don't appear to be physically leaking, but they should at least be tested and replaced if necessary.

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 7:19 pm
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Again, the tube was likely broken while stored. It didn't pop when powered on. The white powder inside is evidence that the tube was powered on after breaking. Are you saying that it is impossible that someone else could have had access to the amp and moved it, or knocked it over?

Capacitor fluid doesn't leak upward, due to gravity it will flow down and onto the board. Was the amp stored upside down?

Whatever you do, check components and don't just start replacing everything because you "feel" that something happened.

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Post subject: Re: My '68 Bandmaster Reverb now blowing fuse, GZ34 is Arcin
Posted: Sat Aug 25, 2012 8:07 pm
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The AA1069 revision was finalized and approved for production in October of 1969 -- hence the "10" (denoting October) and the "69" (designating the year).

The leaky bypass caps do look wonky -- I would replace them, if only for my own peace of mind.

Arjay

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