# Need help with an old Garnet



## davesvintage (Mar 31, 2009)

I have a Garnet 5 P-T Tremelo model that is badged as a Piper. It had a nasty 2 prong lead and I want to convert it to a 3 prong safely. It doesn't have transformer but it looks like a tube rectifier. The active goes straight to the fuse then into a tube then onto the power light via a resistor . The neutral goes from the lead into the on/off switch to the other side of the power light and then onto the centre pins of each control pot. I have removed the dreaded death cap and I put a 3 prong lead on with the ground wire going to the chassis. I believe this circuit has a common ground and the jacks are the only components that are grounded to the chassis. The amp buzzes like crazy but there are no stray voltages to the chassis and jacks. 

I would like to convert this to a safe 3 prong lead and get rid of that nasty buzzing, anyway advice here?

Cheers Dave.


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## fraser (Feb 24, 2007)

is it still zapping you with the 3 prong installed?
i have 2 transformerless amps, but i added iso trannies.
ive had guitar related shocks in the past cause me an irregular heartbeat, that cant be good lol. 
so i played it safe.
if no more shocks, perhaps it needs new filter caps?
the amps i mentioned do have an audible hum at idle- but you cant hear it when im playing, so i ignore it.
seems they used the piper name on a number of different amps- 
sorry man, im not very helpful lol.


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## Wild Bill (May 3, 2006)

davesvintage said:


> I have a Garnet 5 P-T Tremelo model that is badged as a Piper. It had a nasty 2 prong lead and I want to convert it to a 3 prong safely. It doesn't have transformer but it looks like a tube rectifier. The active goes straight to the fuse then into a tube then onto the power light via a resistor . The neutral goes from the lead into the on/off switch to the other side of the power light and then onto the centre pins of each control pot. I have removed the dreaded death cap and I put a 3 prong lead on with the ground wire going to the chassis. I believe this circuit has a common ground and the jacks are the only components that are grounded to the chassis. The amp buzzes like crazy but there are no stray voltages to the chassis and jacks.
> 
> I would like to convert this to a safe 3 prong lead and get rid of that nasty buzzing, anyway advice here?
> 
> Cheers Dave.


The buzz is likely filters but I am concerned about your removal of the "death cap". In most transformerless circuits you NEED it! In fact, I suspect you've made things MORE dangerous! Every circuit that I've seen for a transformerless amp means that if you put in a 3-wire cord you HAVE to use an isolation transformer!

With a transformer amp, the death cap is the one on the ground reversal switch. If it shorts, it allows line voltage on the chassis.

In a transformerless circuit, the real ground is totally isolated from the chassis, EXCEPT for a 'death cap' that connects the chassis to that circuit ground! That cap keeps line voltage off the chassis but makes sure that as far as the signal and circuit goes the chassis is also grounded (through the cap). The chassis needs that grounding to keep out hum! Again, if the cap shorts you get full line voltage on the chassis.

For this reason I never take the death cap out of transformerless amps unless I put in an isolation trannie. You don't absolutely have to have a 3-wire cord to be safe! Possibly millions of old amps, tvs and radios in the Golden Years of tubes used 2 prong transformerless circuits with 'death caps' and we didn't see people routinely dying like flies all around the neighbourhood! They did have electrical safety codes in those days, you know!

I often will just change out the death cap with a new cap of a 600 volt rating. The chances of it failing in a 120 vac application are VERY slim!

Anyhow, something for you to check. If I'm right, you have modded IN your hum! What's more, suppose you plug that 3-wire cord into a socket where some hack artist reversed the black and white wires? If your chassis is has one side of the line voltage grounded directly through the input jack ground then it will be hot!

WB


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## zontar (Oct 25, 2007)

Hmm, I have an older two prong Garnet that sounds like this one.
But I don't sue it anymore.
Maybe I'll just sell it or give it away to someone who can deal with the two prong thing...


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## fraser (Feb 24, 2007)

zontar said:


> Hmm, I have an older two prong Garnet that sounds like this one.
> But I don't sue it anymore.
> Maybe I'll just sell it or give it away to someone who can deal with the two prong thing...


an isolation transformer isnt expensive, or hard to install
i got mine for about $20 bucks apiece.
but feel free to give me your amp-


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## zontar (Oct 25, 2007)

Well, you'd have to come & get it...


But thanks, I'll check that out if I decide to start using it again.
I think my Garnet bass amp is two prong as well, but I've been lending that out for a while, I may be getting that back soon.


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## davesvintage (Mar 31, 2009)

*Garnet amp*

Thanks for the input guys, I am going to replace the filter caps myself and get an amp guy to look at the rest. I am guessing the amp is a 1960 since one of the pots is a CTS dated 1960 so those caps are old. The "Death cap" was leaking what looked like oil so I will definately replace it. I will take your advice Wild Bill but I think this a job for an amp guy, I build and repair guitars and they can only kill you if they fall out of trees. 

Fraser and Zontar I am sorry to say I think I will keep the old girl but thanks for the offer.

Cheers Dave.


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## zontar (Oct 25, 2007)

Well I wasn't after your amp-have my own--but yeah--they can be cool.


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## WannabeGood (Oct 24, 2007)

fraser said:


> an isolation transformer isnt expensive, or hard to install
> i got mine for about $20 bucks apiece.
> but feel free to give me your amp-


Hey Fraz,
Would be interested to know what you bought and where you bought. Need me one or two.

Regards,


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## fraser (Feb 24, 2007)

WannabeGood said:


> Hey Fraz,
> Would be interested to know what you bought and where you bought. Need me one or two.
> 
> Regards,


hi WannabeGood,
what i used was hammond 169QS- 115/115 40VA transformers.
if i recall, they were about 22 bucks each after tax.
i dont know if they are ideal for this, but they are small, and they work fine.
i just went into the local electronics store, talked to the guy, explained that i needed isolation transformers, and why i needed them, and he ordered them for me.
these appear to be readily available online however.
like i say, these were easy to install, and small enough to fit to the chassis(chassies, chassi, chassises?) i was using-


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## WannabeGood (Oct 24, 2007)

Thanks Fraser. I'll be checking them out.

Regards,


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## greco (Jul 15, 2007)

WannabeGood..the Hammond catalog specs these iso transformers as follows:

*Model..................VA (=watts)...... Secondary current in ma.*
169PS..............................15.............................130
169QS .............................40............................260
169RS .............................60............................435 
169SS .............................90............................650

I'm wondering if the secondary current max. is the main consideration, as the VA (watts) seem quite "generous" for these small amps.

Cheers

Dave


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