Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Mon 09, 2019 10:35 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 57 posts ]  Go to page 1, 2, 3  Next
Author Message
 Post subject: found an old Gibson Amp can't find model #
PostPosted: May Tue 21, 2019 12:08 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
found this cool old amp on the FB market page the guy wanted only 100 bucks so I was on it like PBJ on a 5 year old
can't find a model number ,,,,,any of you guys know what it is

Image

Image

Image

Image

Image

I have not tried to power the thing up at least until I know what I got .looks pretty old and seams to be all there .


there is a hand written number on the speaker and the back of the amp. not sure what that's about

Image

Image

and there was this newer mike inside the amp but I don't think its original

Image
Image


Last edited by blainenbecky on May Tue 21, 2019 12:35 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: May Tue 21, 2019 12:17 am 
Member

Joined: Sep Tue 15, 2015 1:16 am
Posts: 692
Location: 18424 PA
Don't power it up until the filter caps are at least changed. You burn out a transformer you will probably never find one.
http://prewaramps.org/

Could be a Gibson, but they were known to change things a lot calling it the same model number. Also check and see if it another amp in a Gibson case.

Maybe a EH-125

Here is a picture of the same amp.
http://jedistar.com/geib-2/


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: May Tue 21, 2019 12:42 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
roger that n3uvt I checked out Gibson EH-125 on eBay and a few of them came up.its looks like the same amp.
mine seams to have a few differences like the amp is in the middle of my cabinet and the ones on ebay are offset to the side for some reason and the speaker wires are on the other side but still it looks like I may have a Gibson EH-125


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: May Tue 21, 2019 5:14 am 
Member
User avatar

Joined: Nov Fri 10, 2006 12:24 am
Posts: 2521
Location: Thornhill, Ontario, Canada
n3uvt wrote:
Don't power it up until the filter caps are at least changed...
+1
Cheers,
Roger

_________________
Roger Jones,
Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Tue 04, 2019 12:06 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
thanks for the info guys,I finally found a little time to get a better look in the thing and I am finding something weird.
on the speaker there is a transformer or choke mounted on it.there is 2 raw copper single strand wires coming out of the coil.and there is 2 newer wires crudely wired on to the 2 old wires about a foot long that go no where. anybody know where these 2 wires are supposed to go ? and when I got into the amp I saw orange gumdrops.question,,,,,did they have orange gumdrops back in the 30's?

Image

Image

Image

Image


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Tue 04, 2019 3:36 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5015
Location: Vancouver Island, Canada
Those orange and maroon capacitors are new, or certainly newish, and probably OK if they are correct values for the circuit.
The old large paper caps are the main concern, as they are filters for the power supply, carrying something in the realm of 350 DC volts. The new caps you will install are much smaller but also much better quality, They are polarized electrolytics and the correct polarity is vital.

That amp is impressive, having push-pull output tubes and 3 more tubes in front of them. The large tube is the rectifier.
A good test is to apply power minus the rectifier tube. Then measure the voltage at the rectifier socket, and watch for excessive heat by touching the power transformer.

The transformer on the speaker is an output transformer. Also a precious component, so take good care of it. Somebody spliced new wires onto it to drive another speaker, I think. Clip those new wires off and make sure you have two good connections there going to the speaker.
Using a DMM set to Ohms, measure the resistance between those 2 soldered stubs where the wires were clipped off.
Maybe the speaker is blown, wouldn't be surprising, but there is an easy test, with a AA battery. Attach wires to the short stubs where the wires were attached to the speaker and touch the other ends to the battery. You should hear a click and see the cone move, out or in, doesn't matter. No reaction, you have a blown speaker coil.

Those wires are not raw, they are insulated with varnish. If the tinned ends snap off, the varnish needs to be carefully scraped off to make a new soldered connection. Work carefully as those wires become brittle and can snap off at the coil end.
The 3 thicker wires coming from the amp go to the primary of the output transformer, one from each power tube and one common connection. Don't operate the amp without a speaker load.
If the speaker sounds bad, or is blown internally, it can be rebuilt. Save it.

The fuse should be a 1 amp slo-blo, so check it as well. It is common to see a 5, 10, or 15 amp fuse in there which is not going to protect things from going up in smoke.

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Tue 04, 2019 11:59 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
thanks for the help westcoastjohn.I will check for these things and hopefully the girl still has a little life in her


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Tue 04, 2019 2:43 pm 
Member

Joined: Aug Sun 23, 2015 6:01 pm
Posts: 1009
Location: South Jersey East of Philly
My guess is that speaker is not a PM one, but is electro-magnetic and has a field coil also. That would have to be checked out too since the field coil is part of the B+ circuit. A possibility is if the voice coil is bad, they added the 2 wires from the output tranny secondary to add a working PM speaker, while still keeping the field coil on the original speaker in the circuit to keep the amp working.


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Fri 07, 2019 4:17 am 
Member
User avatar

Joined: Dec Sat 24, 2011 9:17 pm
Posts: 5015
Location: Vancouver Island, Canada
Right, looking at the pics, there are 2 wires going to the field coil, so that is a likely scenario.

The speaker is going to need to be repaired or replaced. In the meantime, a PM (permanent magnet) speaker that can handle at least 10 Watts, 20 would be better, can be subbed in there, and a choke can be installed to replace the field coil.
Tell us what the power tubes are, and measure the resistance of the speaker field coil. A resistor might take the place of the field coil, maybe with some additional filtering.

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
[:l>)


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 2:23 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
OK guys ,,after reading over your post a few times I think I am getting it.I am a novice at best but I have got a few projects under my belt but still a novice at best.I recapped an old Fender bandmaster here few years beck and it came out great with some help from some very nice folks.this project seems a little more involved but I think my scope just may be enough with some help and I thank any and all who might pitch in with your thoughts.I think understand what went on with the guy hooking up another speaker on to the wires ,I put a meter on the ohm setting on the old speaker terminals and it comes back as 5.9 or 6.0 so I am assuming the voice coil is still good ?
some pic.s as I go

Image

Image

Image

Image

the grand kids came in so I had to shut it down for today but I see where the guy had cut the 2 wires going into the speaker can, tomorrow I will take the back off the speaker and see if I can find why its not working. it sure would be nice if it world be something easy


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 2:35 am 
Member

Joined: Sep Tue 15, 2015 1:16 am
Posts: 692
Location: 18424 PA
May be a replacement speaker with a field coil, so it all may be good. Still, do not power it up with the rectifier tube out, just recap it before you do anything. There's many web forums who deal in old guitar amps, these guys know much more than here on this subject. Like i said before, you burn out the power transformer you will never find a exact original one. If you want to do a step by step repair, come over to aguitarforum.com.


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 12:22 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8200
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Maybe this will help a bit. It "looks" similar to your tube lineup. It might be close enough to help guide you a bit thru' the troubleshooting steps

https://el34world.com/charts/Schematics ... _eh125.pdf


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 2:46 pm 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
thanks for the input guys
I took off the rear speaker cover and un-twisted the 2 wires coming from the coil and put the meter on ohms and it comes back as 1.200 so do you think that points to the coil being still good ? and my tubes seem to be the same as the PDF there bro
some pic's

Image Image

Image Image

and thanks again for all thoughts I am rereading all post and trying my best to come up with the best plan of attach to get this thing up and running,,I know I may be putting the cart before the horse but I really would like to get the speaker going first as I would like to keep the amp looking original as possible.I do realize the amp mush have new Caps as not to though off the voltages . but I will do my best to keep the old amp at least looking right


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 3:17 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4866
Location: Gainesville, Florida
for reference that would be 6SQ7. someone did some poor wiring and repair. could use some heat shrink over bare connections. jumping old electrolytic filter capacitors with replacement is not good practice. you will need to find a better way to terminate new filter capacitors


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 3:35 pm 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
tubeAMP wrote:
for reference that would be 6SQ7. someone did some poor wiring and repair. could use some heat shrink over bare connections. jumping old electrolytic filter capacitors with replacement is not good practice. you will need to find a better way to terminate new filter capacitors



roger that bro I will use heat shrink tubing on the wires and try to make it all look better .
dude, when you say (jumping old electrolytic filter capacitors with replacement is not good practice.)
am I to understand that they may have left the old Caps in place and just put the newer Caps on top of them?


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 4:02 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4866
Location: Gainesville, Florida
actually Im sorry that looks like a socket where the paper tube capacitors are connected :oops:


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sat 08, 2019 9:40 pm 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
tubeAMP wrote:
actually Im sorry that looks like a socket where the paper tube capacitors are connected :oops:


roger that dude ,them Caps look old as the hills


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sun 09, 2019 1:33 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
did some research on youtube on how to test a field coil speaker,it seems I can use an outside voltage source of 12 volts or so to energize the coil magnet ,,,,,and then I can inject a signal on to the voice coil wires to confirm if it is working or not ,sounds simple enough but for some reason there is (3) wires going to the electro magnet coil .my question is why 3 wires and which 2 wires do I put the 12 volts in to charge the magnet ?
see pic

Image

this pic numbered
Image

I can't see where the 3 wires are on this chart

Image


Last edited by blainenbecky on Jun Sun 09, 2019 2:34 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sun 09, 2019 2:30 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 8200
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
If you look at the schematic PDF, you'll see it's "push pull" output. That style of system uses three wires to the OP transformer, the one you have labelled 1, 2, 3.

Your numbers 4, 5 are the output from the OP transformer to the voice coil.

To test your speaker you need to energise the two wires that go into the field coil under the coil dust cover. Then you can send you signal from an audio generator to wires 4,5.

EDIT :: I am going to ask this so that we know what your level of knowledge is. Please don't be offended. Can you read schematic? Do you understand the basics of amplifiers, transformers and speakers?

cheers


Top
 Profile  
 
 Post subject: Re: found an old Gibson Amp can't find model #
PostPosted: Jun Sun 09, 2019 2:51 am 
Member
User avatar

Joined: Apr Sat 28, 2012 11:22 pm
Posts: 560
John Bartley wrote:

EDIT :: I am going to ask this so that we know what your level of knowledge is. Please don't be offended. Can you read schematic? Do you understand the basics of amplifiers, transformers and speakers?

cheers


not at all offended bro and thanks for asking ,I understand this stuff can be very dangerous and I put safety very high on my list of things to live and die with .I am a novice at best,I do have a pretty descent work shop with a lot of testers and stuff I got from an estate sale some years back.
I did save an old 1962 fender bandmaster from a flood 2 years ago with the help of some very nice folks,here is a link to the thread
viewtopic.php?f=13&t=308178&start=160
that amp is still playing strong .I can not read to good the schematics but I can make out some of it .I don't really do this a lot other then change out the occasional bad Capacitor or tube.I try to read these post until I have a pretty good understanding of what you guys are saying before I make a move.
and thanks again for any ideas and thoughts you guys have .


Top
 Profile  
 
Post New Topic Post Reply  [ 57 posts ]  Go to page 1, 2, 3  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB