Rock Amp (70's SS guitar amp)

pigsnoot · 14th June 2009, 01:48 PM

I've got this great little guitar amp, It goes way too loud for It's size and it gives a biting harsh fuzz sound when cranked wich I like a lot!I think It's solid state, but there are also opamps on the board...

Now like a lot of the old amps It's a 2 prong plug, not grounded
(I think that's the reason of the hum it's producing....)

I want to relocate the plug and use standard 3 core plug so there's no power cord attached anymore...

I'd like grounding to the chassis,but there's already stuff connected to the chassis, one wire from the transformer wich is also connected to a cap.....

So is it safe to just ground the chassis to my 3 way power plug I like to install?

I'm no engineer, so I hope this question isn't too silly for you guys...

I just don' want to blow this cute amp, and ofcourse don't want to risk any shocks!!!!

pigsnoot · 14th June 2009, 02:26 PM

Another version I found on he web...
These seem to be quite rare, but not very expensive ...

jaycee · 14th June 2009, 02:32 PM

In one of your pictures the line cord is shown and is clearly 3 core.

It's more likely someone just fitted a 2 prong plug.

pigsnoot · 14th June 2009, 05:56 PM

Quote:

Originally posted by jaycee
In one of your pictures the line cord is shown and is clearly 3 core.

It's more likely someone just fitted a 2 prong plug.

No no I've put that cord in there, ready to be soldered!
The original Is already gone....
I'm just waiting for a go on soldering chassis to earth ground....

jaycee · 14th June 2009, 08:51 PM

Hm, it looks like it's a single ended supply amp, so the case will be attached to the transformers 0V tap. Earthing it will probably cause more problems than it will solve.

My guess is that the humming is caused by that 2200uF 50V capacitor, which is most likely the power supply filter capacitor, now being old and worn out. Another source of hum could simply be the transformer field being picked up by the fact that it's mounted right on top of the chassis with the circuitry in!

AS you don't have much electronics experience I'm not sure how to advise you further, but I wouldn't advise connecting an earth. You COULD however, still add an IEC socket, this is easy enough to do.

pigsnoot · 14th June 2009, 10:37 PM

Thnx...I hope replacing the cap will solve the issue....
So the earth pin of he IEC socket will remain unused?
Isn' there any risk of recieving shocks when plugging in your guitar and singing in a Microphone?

jaycee · 14th June 2009, 11:40 PM

To get a shock the transformer's insulation would have to break down and the primary short to the secondary.

Without examining the amp in greater detail it's hard to say how to correctly apply earthing to this unit. The power supply will most likely require some revision to make this work correctly.

I'm wondering where that ceramic cap that's been hot glued down is going. If the other end of it is connected to the Neutral wire of the power cord - take it out!

unclejed613 · 15th June 2009, 12:15 PM

brown to the power switch, blue to the other termimal that the power cord went to (most likely to the other power transformer wire), and the green/yellow to the ground lug. leave the ceramic cap where it is. replace the power supply cap. the unit probably needs other caps replaced, but one step at a time.

so the cable should connect:
brown to the power switch, power switch then goes to the fuse, fuse to the transformer.

blue wire then goes to the other wire from the transformer, and possibly the ceramic cap.

G/Y wire to the ground lug. leave a couple extra inches of wire on the ground.

chiliD · 23rd July 2009, 11:37 PM

Sorry I'm late to the party.

I found this site when doing a search for Rock Amps.

I had one of the original ones from back in the '70s...if my recollection is accurate, I had serial #18.

I took mine on tour with me to Canada in '81 and got the greatest tone from it (at the time, anyway).

Seeing photos of them again really makes me miss my old one (I'd sold mine when I got back from the tour in '81...regret ever getting rid of it!)

Sorry for the thread hijack.

gain-wire · 24th July 2009, 03:07 PM

Holy Cow! I never thought I'd see someone post a picture of a rock amp! Is that a ten inch speaker?

"Gadzooks, what a tone!"

gimme a day, I'll explain...

15th June 2009, 12:15 PM	#8
unclejed613 diyAudio Member Join Date: Dec 2006	brown to the power switch, blue to the other termimal that the power cord went to (most likely to the other power transformer wire), and the green/yellow to the ground lug. leave the ceramic cap where it is. replace the power supply cap. the unit probably needs other caps replaced, but one step at a time. so the cable should connect: brown to the power switch, power switch then goes to the fuse, fuse to the transformer. blue wire then goes to the other wire from the transformer, and possibly the ceramic cap. G/Y wire to the ground lug. leave a couple extra inches of wire on the ground. __________________ Vintage Audio and Pro-Audio repair ampz(removethis)@sohonet.net spammer trap: http://www1284177414881.v-dc.net/

24th July 2009, 03:07 PM	#10
gain-wire diyAudio Member Join Date: Nov 2004 Location: NCR	Holy Cow! I never thought I'd see someone post a picture of a rock amp! Is that a ten inch speaker? "Gadzooks, what a tone!" gimme a day, I'll explain... __________________ Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig

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14th June 2009, 01:48 PM	#1
pigsnoot diyAudio Member Join Date: Jun 2009	Rock Amp (70's SS guitar amp) I've got this great little guitar amp, It goes way too loud for It's size and it gives a biting harsh fuzz sound when cranked wich I like a lot!I think It's solid state, but there are also opamps on the board... Now like a lot of the old amps It's a 2 prong plug, not grounded (I think that's the reason of the hum it's producing....) I want to relocate the plug and use standard 3 core plug so there's no power cord attached anymore... I'd like grounding to the chassis,but there's already stuff connected to the chassis, one wire from the transformer wich is also connected to a cap..... So is it safe to just ground the chassis to my 3 way power plug I like to install? I'm no engineer, so I hope this question isn't too silly for you guys... I just don' want to blow this cute amp, and ofcourse don't want to risk any shocks!!!!

14th June 2009, 02:26 PM	#2
pigsnoot diyAudio Member Join Date: Jun 2009	Another version I found on he web... These seem to be quite rare, but not very expensive ...

14th June 2009, 02:32 PM	#3
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	In one of your pictures the line cord is shown and is clearly 3 core. It's more likely someone just fitted a 2 prong plug.

14th June 2009, 08:51 PM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Hm, it looks like it's a single ended supply amp, so the case will be attached to the transformers 0V tap. Earthing it will probably cause more problems than it will solve. My guess is that the humming is caused by that 2200uF 50V capacitor, which is most likely the power supply filter capacitor, now being old and worn out. Another source of hum could simply be the transformer field being picked up by the fact that it's mounted right on top of the chassis with the circuitry in! AS you don't have much electronics experience I'm not sure how to advise you further, but I wouldn't advise connecting an earth. You COULD however, still add an IEC socket, this is easy enough to do.

14th June 2009, 10:37 PM	#6
pigsnoot diyAudio Member Join Date: Jun 2009	Thnx...I hope replacing the cap will solve the issue.... So the earth pin of he IEC socket will remain unused? Isn' there any risk of recieving shocks when plugging in your guitar and singing in a Microphone?

14th June 2009, 11:40 PM	#7
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	To get a shock the transformer's insulation would have to break down and the primary short to the secondary. Without examining the amp in greater detail it's hard to say how to correctly apply earthing to this unit. The power supply will most likely require some revision to make this work correctly. I'm wondering where that ceramic cap that's been hot glued down is going. If the other end of it is connected to the Neutral wire of the power cord - take it out!

23rd July 2009, 11:37 PM	#9
chiliD diyAudio Member Join Date: Jul 2009	Sorry I'm late to the party. I found this site when doing a search for Rock Amps. I had one of the original ones from back in the '70s...if my recollection is accurate, I had serial #18. I took mine on tour with me to Canada in '81 and got the greatest tone from it (at the time, anyway). Seeing photos of them again really makes me miss my old one (I'd sold mine when I got back from the tour in '81...regret ever getting rid of it!) Sorry for the thread hijack.

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