Rescued Gibson BR-6 from Barn

[yorgle]

Just picked this up yesterday- it was stored in a horse barn for the past 35 years!  As you can see, it's rough, but I plan to get it cleaned up and working.

[yorgle]

Yikes!  Luckily, nobody was home! 

[yorgle]

Seemingly original field coil speaker but absolutely no trace of the cone!  It's like it simply dissolved over the years.  Until I can get this replaced or repaired, can I temporarily insert an appropriately sized resistor in place of the field coil and use a regular speaker while working on the amp?

[shooter]

nice barn find, and the cone, dissolved alright, in the mice bellies 


I just now got outta the shower after spending 2hrs in the attic cleaning up the squirrel, bat, mice, motherload
now 3-4 days of sealing up 
life on the farm 

[sluckey]

Seemingly original field coil speaker but absolutely no trace of the cone!  It's like it simply dissolved over the years.  Until I can get this replaced or repaired, can I temporarily insert an appropriately sized resistor in place of the field coil and use a regular speaker while working on the amp?

yes

[yorgle]

Thanks, Slukey.  Here are some pics of the chassis, before and after a first round of cleaning.  The weight of the PT had bent the back edge downward over the years, but I was able to bend it back easily enough.  I think I might add a bit of bar stock along the back to give it some extra support.  Round two of cleaning will be involve some wire brushing and naptha. 

[shooter]

That has got to be one of the best barn finds ever!
I'd take that over 12 pcb, brand new shiny things any day
enjoy the process, what you put in comes back 10 fold 

[Raybob]

Yikes!  Luckily, nobody was home!

Speaker cones make for warm nests.   

[tubeswell]

Cool find!

[bmccowan]

Nice find. I really like that amp. Have rewired a BR-6F which had a pentode 6SJ7 for v1 instead of the 6SL7 that your amp likely has; and converted a Webster Conn Organ amp to a BR-6 circuit with 6L6s. Its raw tube sound all the time - no tone stack to muck things up. I used a 1K 5W resistor as the FC speaker was shot - worked fine. It's a Gibson so you may find variations from schematics.

[yorgle]

After two naphtha baths and a couple of hours with wire brushes the chassis is as clean as reasonably possible short of totally disassembly and sandblasting, which I’m not inclined to undertake.  There is still a faint scent of mouse poo, but I expect that will fade away in time.  The top and power transformer will be easy enough to paint, but I don’t think there’s much I can do about the silkscreen on the face. Underneath, a lot of the paint washed off, but it’s clean and I’m just going to oil it so it doesn’t rust.

[PRR]

> The weight of the PT had bent the back edge downward over the years

Not "over the years". Sag in 1000 year old iron is hard to prove.

It "sagged" when they dropped it off the truck that one (or two or ten) time(s).

[bmccowan]

You got that pretty clean - I've had limited results removing rust with Quick-Glo. If used carefully you can get off some of that faceplate rust without harming the logo and other graphics. But from what I've seen, all old Gibsons look similar unless they've been stored in a closet in Arizona. Another auto product that I've used recently to clean amps is Car Guys Super Cleaner - I suspect it might take care of the remaining mouse poo odor. I used to use a product called Big Bath, but have had a hard time finding it lately.

[yorgle]

You got that pretty clean - I've had limited results removing rust with Quick-Glo. If used carefully you can get off some of that faceplate rust without harming the logo and other graphics. But from what I've seen, all old Gibsons look similar unless they've been stored in a closet in Arizona. Another auto product that I've used recently to clean amps is Car Guys Super Cleaner - I suspect it might take care of the remaining mouse poo odor. I used to use a product called Big Bath, but have had a hard time finding it lately.

Thanks for the suggestions, but I don't think I'll risk any further cleaning of the faceplate because the lettering is so fragile and for all practical purposes, irreplaceable.  I used a fine steel brush to remove most of the bumpy/flakey rust from the front and my plan is to "dust" some flat black paint over those spots, blending it into the surrounding black areas as much as possible.  I'm debating whether or not to then shoot some semi-gloss or even flat clear over the face to protect the lettering from further wear.  Doing that will, of course, effectively eliminate the possibility of further restoring it down the road, but I think this one is just too far gone to shoot for a total restoration. 

I'll give the Car Guys Super Cleaner a try on the cloth wiring which I believe is where the remaining oder is hiding. 

[bmccowan]

And I should clarify that most Gibson face panels end up looking like that - not the rest of the chassis. And have you ever tried Flood's Penetrol? Its a pretty good rust preventative and would add a reversible matte coating on the panel. Takes a while to dry though.
On mice. Several years ago I bought a 50's Valco/Gretsch amp on Ebay. Seller said it "worked great - sounded awesome." I pulled the chassis and most of the wiring was destroyed and an electrocuted mouse had its jaw around a B+ wire. I contacted the seller who insisted that it worked great just before he packed it. So apparently the mouse snuck in just as it was being packed; chewed the wires during shipping; and the UPS driver opened the box; plugged in the amp and zapped the poor fellow. Taped er all back up and delivered it. As Judy Tanuta used to say, "hey, it could happen."

[shooter]

an electrocuted mouse had its jaw around a B+ wire.

my house has 1 run that I left tube n knob, just because.  below the wires are many bones of unknown small critters 
now-a-days they run freely in the attic, maybe the 'ol days were better 

[bmccowan]

Now they just trip the GFCI, eh?

[tubeswell]

... don’t think there’s much I can do about the silkscreen on the face.

Maybe take a photo of the faceplate and then use that to inform a new panel drawing in autoCAD and then get a new sheetmetal one screened that can cover the old one?

[shooter]

 
no gfi on that run, every now and then I have to reset the breaker 

[yorgle]

Finished the face last night.  I used acrylic flat black and brown paint to painstakingly “stain” all of the dark and rusty areas to a uniform flat color.  The white printing is actually raised a tiny bit from the surface which made it easier to get nice clean edges.  I briefly toyed with the idea of trying to recreate the missing silkscreening, but decided to stay with my worn, but clean theme.  Once done, I sprayed it with two light coats of semi-gloss acrylic clear to protect it from further deterioration.

[shooter]

very nice 


now you need a cool Rat-Rod with a pure sine wave inverter, couple 12" and hit the outdoor small circuit concert road 

[tubeswell]

Yes very nice indeed. Very professional looking better than ‘relic-ed’ (and it’s a real relic‘n’all)

[yorgle]

Thanks.  Overall, I'm happy with the results- especially compared to what it was.  Here are some closeups of the partially painted dial area that give a good before/after comparison:

[66Strat]

very nice 


now you need a cool Rat-Rod with a pure sine wave inverter, couple 12" and hit the outdoor small circuit concert road 

Maybe add in a white sport coat with a pink carnation?

[yorgle]

very nice 


now you need a cool Rat-Rod with a pure sine wave inverter, couple 12" and hit the outdoor small circuit concert road 

Maybe add in a white sport coat with a pink carnation?

You guys are giving me some good ideas...

[bmccowan]

Wow! came out great. I'm sending you all my rusty amps.

[yorgle]

Wow! came out great. I'm sending you all my rusty amps.

Thanks. Now let’s see what can be done about this:

[sluckey]

I'd start by measuring the resistance of the field coil and OT primary/secondary.

[yorgle]

I'd start by measuring the resistance of the field coil and OT primary/secondary.

Field Coil:  1.2k
OT primary:  549
      Secondary:  .5
Speaker coil:  3

[bmccowan]

That 1.2K agrees with the schematic (1K) so that's good. you could get that speaker reconed, or get a kit and do it yourself. Can partially see the code in the photos and I think it's a Utah speaker. But in the meantime, I'd be tempted to put a 1K 5W resistor and use a PM speaker. Some folks say there is sonic mojo in the field coil, but I've never heard it; even when I had my mojo workin'. Looks like a mouse attacked the OT, eh?

[yorgle]

Fortunately, the mouse only took a few nibbles and apparently decided he didn’t like the taste.  I’m going to try re-coning the speaker myself, but in the meantime I’ve got an old 4 ohm Epiphone 8 inch to use while I get the amp up and running.

 On that note, I installed a three-prong power cord and a 1k, 5 watt resistor in place of the field coil, and stuck in some temporary filter caps and, good news, it worked, and sounded good!  B+ was 349vac, 275 at the screens.  But... after 5 minutes or so I started smelling wax other hot smells so I stopped measuring and discovered that 1) the PT was bubbling hot, and the 1k resistor was turning brown.  The PT has an internal short.  Luckily, I have another similar spec PT on hand that fits the chassis closely enough so that problem is solved for now.  I’ll eventually have the original one rebuilt, so I can keep this beast as original as possible. I guess I’ll have to order a 10 w resistor before I go ahead with more testing.  In the meantime, I gave the cabinet a hearty scrubbing tonight and am going to start gluing down the loose tolex. 

[PRR]

Browning the 1K resistor does not point to the PT but the tubes or caps sucking too much.

[yorgle]

Browning the 1K resistor does not point to the PT but the tubes or caps sucking too much.

Yeah, I’m confident that they are unrelated issues.  The PT bubbles even when all of the secondaries are disconnected and I can actually hear something angry and sizzlin’ inside as soon as it’s hooked up to mains.  The 1k most likely toasted because it was only 5w and probably should be at least 10w.

[PRR]

> probably should be at least 10w.

This is a two 6V6 amp? So sucks 80mA-100mA. 0.080A to 0.100A.

0.1A^2 * 1k is 10 Watts right there. So a 10W part may not last a month (and a 5W may be toast before breakfast). 20W (or several smaller parts together) is reasonable.

[yorgle]

How about two 7watt 500r in series?  I’ve got those koolohms from my last project sitting here.  That should last until I get the field coil re-coned, or at least until after breakfast.

[HotBluePlates]

How about two 7watt ... in series?  ...

0.1A^2 * 1k is 10 Watts right there. ... 20W (or several smaller parts together) is reasonable.

The rule of thumb is take the known-dissipation, then use a resistor rated for double that dissipation.

Do it right the first time, and you won't have to buy another resistor later...

[yorgle]

Since the original wires from the chassis to the field coil/OT/speaker were chewed up by rodents, what do you guys think about using this connector to make servicing more convenient. I would hang the female plug on the chassis side so that if it gets disconnected while the amp is ON, the hot pins wouldn't be exposed. 

[tubeswell]

the PT was bubbling hot, and the 1k resistor was turning brown.  The PT has an internal short. 

Did your PT have the 'spec sheet' attached?


If not, here is a snap from a BR-6F PT (which will be the same as the BR-6)

[yorgle]

No spec tag on mine, but it measured 320-0-320 before I removed it.  I’m going to take the covers off and see if I can find the short. Maybe I’ll get lucky and it will be near the surface. 

[yorgle]

Question regarding filter caps:  when I opened this amp up, I found a 30-20-20 multi-section capacitor (only the 30 and one of the 20's was used for nodes 1 and 2 of the B+ sup).  The third node had its own 10uf cap).  The schematic for the BR6 in the library shows 20, 10 and 10, but I know Gibson frequently deviated from schematics.  I've found pictures of other early BR-6's and they all have the same 10uf cap on the 3rd node so I'm confident that's correct and original.  The can cap, however, I'm not so sure about since the wires from it were not cloth covered like all of the other wiring in the amp.  My question here is this:  right now I have individual 22uf, 10uf and 10uf caps temporarily installed, and am getting just a bit of hum. I have a shiny brand-new JJ 40-20-20-20 can sitting here- would I be likely to fry anything if I stuck that in there instead of the individual caps which are closer to the schematic values?

[shooter]

I don't see a problem, the Rectifier tube has a max cap limit, but 40uF shouldn't violate it too bad 

[bmccowan]

I don't see a performance problem with that either. But that JJ is not designed to be mounted inside a chassis. If you want to stay closer to the original, I'd suggest F&T axial caps. 1-20 and 2-10s; or what i would likely do is put in one 20uf and a double 16 cap. They would fit well inside the chassis. I'd secure them with those pads that take cable ties. Any of these ideas will be a big improvement to what is in there now.
Good luck on that power transformer.

[yorgle]

Well, with a slight bit of persuasion, the JJ can fit in the clamp where the old one sat so that looks all neat and tidy.  Didn't affect the slight buzz.  I realized last night that I actually had a complete 10.5" field coil speaker in an old Philco radio that a client had given to me years ago, and it just happens to measure 1.15K ohms, plus it's got a good cone, so I made an adapter ring to fit it to the Gibson's 10" bolt pattern and its now living quite well inside the cabinet.  I have no idea if it works or not, but tonight I'll swap the Gibson OT onto it, wire it up and find out.

[yorgle]

The old Philco speaker works, but she sounds nasty and spews out an almighty hum.  I've ordered a replacement cone for the original speaker so once that's done, we'll see how it sounds.  Question:  with the OT mounted to the speaker, I've got five wires running about 7 inches from the amp to the speaker- three wires for the OT and two for the field coil.  Should any (or all) of those wires be shielded?

[shooter]

shielded from "who?", they are the biggest signals and highest B+ in the amp.  keep them away from all the small fry n you should be good


maybe twist the 3 Ot together and the 2 power together

[yorgle]

shielded from "who?", they are the biggest signals and highest B+ in the amp.  keep them away from all the small fry n you should be good


maybe twist the 3 Ot together and the 2 power together

I guess I thought all that volts might be sending evil waves to the tubes topside. 

[shooter]

technically you're correct in that any varying voltage through a conductor will cause "evil waves" but the tubes pick up the dirty stuff more through the grids possibly cathodes where all the sensitive electrons live 
so just keep the big dirty from the small sensitive and you are good

[yorgle]

The new cone for the original field coil speaker arrived today and I'm happy to report that my first attempt at cone replacement was a success!  The amp is now back together and making music with high voltages as God intended!