The Acoustic Club

[JacklegBass]

Look good?

That looks pretty good to me. I notice that in addition to eliminating the death cap from the common terminal of the GND/REV switch you would also eliminate the .047 cap across the terminals of the ON/OFF switch. It's been a long time, I think I might have left that one in place thinking it's purpose is to ease the burden on the switch contacts at turn-on and minimize pitting. The power switch is pretty light duty and a bear to replace. If the GND/REV switch shorts it's going to light up the chassis, but if the power switch cap shorts it seems the worst that would happen would be that the amp never turns off. Anyhow, what you have sketched out should work.

 

[chadds]

I stood to close, no wonder I've lost my hearing!

TD

What?

 

[byacey]

That looks pretty good to me. I notice that in addition to eliminating the death cap from the common terminal of the GND/REV switch you would also eliminate the .047 cap across the terminals of the ON/OFF switch. It's been a long time, I think I might have left that one in place thinking it's purpose is to ease the burden on the switch contacts at turn-on and minimize pitting. The power switch is pretty light duty and a bear to replace. If the GND/REV switch shorts it's going to light up the chassis, but if the power switch cap shorts it seems the worst that would happen would be that the amp never turns off. Anyhow, what you have sketched out should work.

Why would you want to remove the cap across the power switch? It's beneficial to protecting the switch contacts.

 

[Roxbororob]

I kept the cap across the rocker switch also (had forgotten this).

 

[JacklegBass]

Why would you want to remove the cap across the power switch? It's beneficial to protecting the switch contacts.

That was my point and why I kept that cap installed to keep the power switch contacts from pitting. I only eliminated the death cap.

 

[LetItGrowTone]

If I'm not mistaken the safest type of cap that goes across a power switch is a different type (designed to fail open, not shorted). It's something like X or Y for different applications. Better Google it.

 

[byacey]

If I'm not mistaken the safest type of cap that goes across a power switch is a different type (designed to fail open, not shorted). It's something like X or Y for different applications. Better Google it.

If that cap fails open or shorted makes little difference from a safety perspective. The ground cap is a different story.

 

[byacey]

That was my point and why I kept that cap installed to keep the power switch contacts from pitting. I only eliminated the death cap.

Sorry, from your post, I thought you removed that cap, too.

 

[JacklegBass]

If that cap fails open or shorted makes little difference from a safety perspective. The ground cap is a different story.

^^^ This is correct. ^^^

 

[LetItGrowTone]

Well, either someone explains it here or we all Google it, because it's important.

 

[Roxbororob]

The rocker switch cap is not connected to chassis ground (like the ground fault "death cap". If it fails open power will not be fed into the ground (and to you). Worst case is the on/off switch will be bypassed and the amp will have to be unplugged to turn it off.

 

[JacklegBass]

Precisely...

 

[byacey]

Actually, if the ground switch cap was left in place after grounding the chassis with a 3 conductor power cord, and the cap went open, it wouldn't make one bit of difference, safety or operationally.

If it shorted, the cap would either burn up, or pop the line outlet circuit breaker, depending which position the ground switch is in.

 

[Roxbororob]

Actually, if the ground switch cap was left in place after grounding the chassis with a 3 conductor power cord, and the cap went open, it wouldn't make one bit of difference, safety or operationally.

If it shorted, the cap would either burn up, or pop the line outlet circuit breaker, depending which position the ground switch is in.

Not sure I would like to test the response time of the breaker (IMO).

 

[MauiMike]

Back in the day my rig kicked. A few years ago I down-sized the cabinet because it was a pain to haul around, but I miss that 18" Ball Buster!

 

[Northern Pike]

I stood to close, no wonder I've lost my hearing!

TD

You lost your spelling too.

 

[Rocker47]

Hello! It took a while, but I found this thread and am hoping to get some help. I just picked up a mid 70's 140 and absolutely love it! Loud, light and I love the tone! I am looking to find the year of production. I can only narrow it down to the years 72-76. With a serial number of 8787 would anyone know how to date it? Thanks in advance!

 

[StereoPlayer]

Hello! It took a while, but I found this thread and am hoping to get some help. I just picked up a mid 70's 140 and absolutely love it! Loud, light and I love the tone! I am looking to find the year of production. I can only narrow it down to the years 72-76. With a serial number of 8787 would anyone know how to date it? Thanks in advance!

My 370 head has the date stamped on the amp chassis inside. I don't know if that's how your head is dated though.

 

[Rocker47]

My 370 head has the date stamped on the amp chassis inside. I don't know if that's I how your head is dated though.

Thank you for the reply! I took the chassis out yesterday to see if there was any markings on it, the boards or the pots and there wasn't a year marked anywhere. There are other numbers on the boards, but none that make sense as a year indicator.

 

[JacklegBass]

Your best chance for narrowing it down within a few months is to find the manufacturing date codes on the pots, large chassis-mounted capacitors, or the power transformer. For example, your pots may have a manufacturing code something like "137-7407" which would indicate they were made by CTS (137) in the 7th week of 1974.