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1970's sears 125-xl amp

Started by LJN, April 16, 2011, 12:12:51 AM

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in what year was the gibson firebird released?

1963
2 (50%)
1958
2 (50%)
1972
0 (0%)

Total Members Voted: 4

J M Fahey

Quotethe reverb is supposedly some kind of wierd piezo type unit. it works, but it's very weak.
Short answer: not, not really.
A slightly longer one:
*everything* can be repaired. even a burnt match, but in this case it would involve building a whole new amp, or thereabouts. Not worth the effort.

LJN

I figured as much. Maybe I'll just get a reverb pedal and put in front of it. Thank you for the advice.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

I would like to add that a schematic for this amp is pretty much impossible to find. I'm not real good at reading them either.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

J M Fahey

There are a couple SS Silvertone amps floating around, a couple of them in the GT Tube amplifiers, no less.
They can't be *that* different.
The basic variations were whether they used an obsolete driver transformer for the power transistors or a more modern, conventional one with driver transistors.
The "technology upgrade" happened around the early 70's so you might have gotten either of them, depending on manufacturing date.


LJN

#19
Wow, I didn't know that. I'm not sure, but I've been thinking it's a '71, could be a '72.never the less, This is the amp I've been searching for my whole life, I just didn't know it until I got the thing working. It's the first amp I've repaired, and it won't be the last. Although the next one will hopefully be a tube amp. I use this old amp every day. I wouldn't trade it for any fender, marshall, or peavey on the market. Now, if I could just get a gibson firebirdV to use with it, that would sound awesome. Thank you all for the advice. How can I tell what year this old beast was made in? also, where can I find some amp covering material? I'd like to dress it up a little. :)
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

J M Fahey

Knowing the exact manufacturing year is not that important, since it's not a collector's item, so you won't get detailed obsessive serial number lists as you will on other luckier ones, but most parts have a date code, I'm certain for insurance or warranty purposes.
Once you find a couple matching ones, you know the amp was made sometime after that.
The typical format is a 4 digit number: the first two show the year and the others the working week, (01 to 52), easy to translate to month.
Read http://www.triodeel.com/eiacode.htm and http://home.provide.net/~cfh/pots.html

A potentiometer labelled A1M 137 7006 should be read as:
"A(udio taper/Logarithmic) Resistance 1M(egohm) made in (19)70, work week 06 (mid February) .
It would probably be found in a 1970 or 1971 made amplifier.
Since electronics parts have looooong shelf life, they may be found in *much* later amps, never in an earlier one (of course), unless installed later in a repair job (which also tells you a story about that "mint ... *never* opened collector's item).
As an example, yesterday I repaired an old 200W Fahey PA amplifier (my brand) , made in 1989 (many parts had 1987/1988 codes) with ST brand 2N3055 transistors code dated 931 (week 31 of 2009), made in Malaysia,  and TWT brand ceramic .33 ohm resistors labelled 902 (week 2 of 2009) , made either in Taiwan or China.
And we are talking a 2011 job, which is reasonable: 2 years from manufacturing to actual use, quite normal for parts which sit some time in a dealer shelf.

As a curiosity, post what you find on yours.

LJN

Tank you very much. I'll see what I can find out when I get the chance. From what I remember, I think the part numbers are of an odd sort, But at the time, I wasn't really looking for that. I'll be looking for them next time,though. There's a volume pot that needs to be replaced. I will write every number down that I see and post them.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

Juan, I just took another look inside the amp. According to what you say about the date codes on potentiometers, these date to 1968. I found two different part numbers on the pots; 1-505-305 6845; and B-302-304 6847.Would that mean this amp was built in 1970? The transistors have 2 different part numbers as well; 2N5133, and 2N4250. I can remember the numbers on the transistors, because I had so much trouble finding replacements. I'll probably have even more trouble finding a replacement volume pot for the old beast. It's the channel 1 volume, I use channel 2.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

J M Fahey

Yes, 6845 and 6847 mean late 1968, compatible with a 1970 amp.
Your volume pot should match value and taper, nothing else.
Well, size too and probably the shaft to use the same knob, but nothing difficult.
Since they were non-switching but two very similar channels, only adding "evffects" to one of them, my guess is they are otherwise exactly alike, so volume pots should be the same.
Check it.
Those other numbers must be internal "house numbers" , but measure the pots with your multimeter and you're done.

LJN

#24
Than you very much, Juan. I finally feel like I've found out some very valuable information on this old beast. I'm very greatful for your advice. I'm going to see if I can find a replacement for channel 1's volume, and hopefully I can order one and fix that. Hopefully, MCM has one. If they do, I can order it and have it in about 3 days. I'd still like to find out what the output is on this amp. I guess it's about 50 watts or somewhere thereabouts. I'm a guy who likes to know as much as possible about his instruments and amps. Thank you all for the replies. If any of you know anything else that migt help, please let me know.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

#25
I just found out that the celestion speaker in my sears amp's cabinet was made on may 13, 1980. It's date code reads EN13. The jensen speaker that accompanies it is most likley a 1961, The date code on it reads; 220144. But it makes no sense, because this is a ceramic magnet speaker. Could they have been making those as early as 1961? :-\ I understand that when the '70's came along, the codes were changed from having 6 digits, to having 7 digits. the later codes apparently show the last 2 digits of the year, insted of just 1. I guess that got rid of some confusion for the '70's and later models. :loco
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

Quote from: J M Fahey on April 26, 2011, 12:07:23 PM
Yes, 6845 and 6847 mean late 1968, compatible with a 1970 amp.
Your volume pot should match value and taper, nothing else.
Well, size too and probably the shaft to use the same knob, but nothing difficult.
Since they were non-switching but two very similar channels, only adding "evffects" to one of them, my guess is they are otherwise exactly alike, so volume pots should be the same.
Check it.
Those other numbers must be internal "house numbers" , but measure the pots with your multimeter and you're done.

I forgot to mention that I dont have a multimeter, but I'm gonna get one as soon as I can. Getting tired of the guesswork. I understand about the pots, and you are right, Juan. the volume pots have the same numbers, but theirs are different then the rest. I'll have to get a multimeter if I'm going to start working on amps and effects, just to be on the safe side. The transistors were easy bacause the amp had been lying opren for so long that each one had a lead that was rusted off. I was still very nervous about plugging it in because it had been rained in, wires were broken(I fixed those first), and it was just in awful shape. The volume on channel 1 broke when I tried to free it up. Channel 1 does work, but it's LOUD. :)
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

I found the original enclosure for the amp head yesterday( well, what's left of it). All I have to do is go back and get it. It sort of fell apart when I picked it up. I also found out where the celestion in the cab came from. My uncle put it there because one of the jensens went bad. He said he had bought the speaker at a flea market about a year before he bought the amp. In his words, something told him He'd need it. He said if he finds the other jensen he'll bring it to me. I sure hope it turns up.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

I went and got the original enclosure to the amp the other day, there's not much left of it, But now I know more about how the control panel was originally mounted. I also found a digital multimeter for $12, and I bought it. I'll be measuring the pots in the amp next time I take it apart.
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL

LJN

I have one more question about this amp. I'm pretty sure it needs a cap job because the bass control doesn't work like it should. I've been playing through it since december, and it still sounds great. My question is; Will it hurt the amp if I keep playing through it? Please get back to me on it.


                                                                                           Thanks, LJN
If it sounds good, USE IT!

Epiphone Les Paul, Kasino U100- P, Sears 125-XL