Gibson EH-150

[chunkitup]

What a Sunday. I just got a lesson in vintage resistors and caps. Crazy Mica caps with three colored dots and stuff like that. Thank God for the internet. Someone gave me this amp to fix. I havent fired it up yet. I just used a schematic online and traced the amp to it and changed anything that wasnt right or wrong. I am attaching it to see if you guys could look it over and make sure everything is alright. Everything is original except for a Mallory cap in the power supply which I really doubt is original from the late 30's or early 40's. I cant stop coughing from the damn dust from this amp. Is there any asbestos in these babies? I was thinking if the scheme is alright that the power tubes which are radiotron 6l6's and probably original may be the culprit just due to being really old. The caps in the amp are aerovox(which are still in biz) and they look fine. I really didnt see any kind of leakage. They are sort of gooey or soft but nothing from the ends of the caps which are axials.
Thanks for any help.

[Gtr_tech]

I'd check *all* those paper coupling caps for leakage. I'd bet they're all way leaky. The electrolytics in the pwr supply should be replaced without even thinking about it. real old amps like that need lots of attention of they're in stock untouched condition. Better ask the owner "how much do you love it?" 'cause it could end up being a ton of work to get it up to par.

[Enzo]

Leakage refers to electrical leakage - the cap has lost its ability to block DC. It is only coincidental that some caps leak internal stuff out the vent or out the ends.

Certainly when a cap oozes out the ends it is bad, but plenty of caps that look like they were made yesterday leak like a screen door.

I will bet my lunch money that every wax covered cap in there needs to be changed. I don;t remember the last time I encountered one that wasn;t.

Mallory has been around forever, so I don;t know why the cap wouldn;t be original unless there is evidence it was chaged out. I suspect all the electrolytics are dried out as well.

Which is pretty much what Gtr Tech said.

[Prairie Dawg]

Leakage refers to electrical leakage - the cap has lost its ability to block DC. It is only coincidental that some caps leak internal stuff out the vent or out the ends.

Certainly when a cap oozes out the ends it is bad, but plenty of caps that look like they were made yesterday leak like a screen door.

I will bet my lunch money that every wax covered cap in there needs to be changed. I don;t remember the last time I encountered one that wasn;t.

Mallory has been around forever, so I don;t know why the cap wouldn;t be original unless there is evidence it was chaged out. I suspect all the electrolytics are dried out as well.

Wwhich os pretty much what Gtr Tech said.

I wouldn't take that bet. I came up with a kit assortment of Cornell Dubilier Cub capacitors that were out of that fifties molded plastic genre. Every last one of them was leaky, and they all went in the trash. Cool as they were I don't keep stuff like that around, just like I don't keep used tubes that don't test at least nominal for a new one.

Plus, you can always salvage the paper tubes and put new stuff inside and pot the ends with wax for appearance.

Got a deal like that going with a recently acquired Federal cathedral radio, circa 1931.

[Enzo]

Lunch is a pretty important part of my day. I don;t wager it lightly.

Wow, stuffing old wax caps and rewaxing them, now THAT is hard core.

I have had occasions where the wax guck was too thick and cloudy to read the parts, so a blast from the heat gun had it draining right off the part. Clean as new then.


The hardest core story I can think of was my pal Stretch over at Elderly. He needed one of those old 5-pin footswitch conectors for some GIbson amp, so he made one. Fashioned the body from some hardwood - maple I think - made up some pins from proper diameter metal rod stock - could have been nails I suppose. Formed nice round ends on them. Ran the pins through the body leaving a space for to solder wires to it. I think it added to the tone even more than those wooden knobs they sell to audiophiles.

[chunkitup]

Ok Ok I will try and sell the owner on changing out all the caps as I agree they need to be updated. I just dont know if he will find it worth it. I want to do it just to see how this amp will sound but I need to make some money. Now what about the resistors? Will they be fine? Also, on the schematic there was one area that I corrected and I was wondering if that looks alright. The last 6C5 feeding the tranny before the pwr tubes.

[Prairie Dawg]

Lunch is a pretty important part of my day. I don;t wager it lightly.

Wow, stuffing old wax caps and rewaxing them, now THAT is hard core.

I have had occasions where the wax guck was too thick and cloudy to read the parts, so a blast from the heat gun had it draining right off the part. Clean as new then.


The hardest core story I can think of was my pal Stretch over at Elderly. He needed one of those old 5-pin footswitch conectors for some GIbson amp, so he made one. Fashioned the body from some hardwood - maple I think - made up some pins from proper diameter metal rod stock - could have been nails I suppose. Formed nice round ends on them. Ran the pins through the body leaving a space for to solder wires to it. I think it added to the tone even more than those wooden knobs they sell to audiophiles.

Being as y'all are in Lansing your buddy might have been able to come up with something from any one of the Michigan Antique Radio Club members. My membership lapsed a while ago when I moved back to the left coast but they're a pretty good bunch of people.

I'm assuming that the five pin pattern was the same as what you'd find on a 24A base. It could be different. Fact is, if it was, you could take a base and make it into a plug.

[Enzo]

The Gibson FS jack is about 5/8-3/4"diameter if I recall, . Same connector Rockola used for volume control on their juke boxes. Not the size of fat pin tube bases.

[melvin]

Restoring an amp like that can be problematic if the owner wants to sell it. It may not sound spectacular even if you get it into original playing condition, at which point it may not be as collectible. So a player probably won't pay $800 plus for a practice amp and a collector might not either due to it now being unoriginal.

But they are actually fun to work on... you may be the first person in 50 years to play it.

So when you get it running, maybe start with some Ritchie Valens? Muddy Waters? Let it get comfortable before introducing it to the 13th Floor Elevators.

[Prairie Dawg]

The Gibson FS jack is about 5/8-3/4"diameter if I recall, . Same connector Rockola used for volume control on their juke boxes. Not the size of fat pin tube bases.

Almost makes you think it has an AN or MS part number. I prolly woulda put a nice cannon plug in there and safety wired it.

[Enzo]

Oh the connector in question is the stock Gibson FS AMphenol 91-MPM5L mating to chassis socket AMphenol 78-PCG5.


Lots of options, I was just impressed he made one.

[booj]

Oh gawd get over it! 10 caps stands in the way of refurbishing a priceless bit of history and your crybabying about a re-cap job.

[melvin]

priceless? if you say so. Nevertheless, if I said "crybabying about a recap job" to a customer, I don't think he/she would take it too kindly.

[chunkitup]

Schematic Verification

Alright I am now ready to rebuild this bit of Gibson History. I am going to replace the eyelet board with a turret board and all caps and resistors with new up to date ones.

What I am asking is if someone more familiar than I am with this old amp could look at the schematic I posted and see if they see any mistakes. I downloaded that scheme and then made all the changes that this amp has in it right now. Please let me know if it is correct or if I need to correct it.
Thanks

[chunkitup]

Someone, Anyone??