WTH have I got here? Tech help wanted. Garage Sale Find.

Hey guys, you may have seen my post in the general amps forum from earlier today. I am looking for some tech help. The best place I know, is you guys on here. I found a Canadian built Garnet guitar amp today at a local garage sale. I am pretty excited about it as it sounds really, really good. From what I can tell it is about a 5W all tube amp. No circuit board. Some real point to point wiring here. Here are some photos of the circuit.

https://lh3.googleusercontent.com/-WXy_m_5CMgs/T6cDQS52IkI/AAAAAAAAA3k/NExy2v4WIiQ/s512/IMGP3533.JPG

https://lh5.googleusercontent.com/-66LJ6SK56Uw/T6cC5Fgl6jI/AAAAAAAAA3Q/QjNxZNvE7QI/s800/IMGP3532.JPG

It has tremolo as you can see. It has 4 tubes. 2qty 7 pin long skinny ones, that are un-marked and I can't identify. It has a 12AX7 and a USA Tung Sol 7 pin 12AV6. I don't see a rectifier tube. The weirdest thing is I cannot find a power transformer anywhere. Have a look at these photos below. I see an output transformer only.
Any idea? Is this a similar circuit to the Fender Music Master Bassman? Is it a push/pull design? Any enlightening info appreciated.

https://lh4.googleusercontent.com/-yamwUwGSeiY/T6cCgHIIoqI/AAAAAAAAA24/1EQLFOk0MFc/s800/IMGP3526.JPG

https://lh6.googleusercontent.com/-mDpkH7fSXA4/T6cChN8qB0I/AAAAAAAAA3I/7Mr1QVsZxtQ/s800/IMGP3525.JPG

https://lh5.googleusercontent.com/-wEXpBCTyhfo/T6cB8d3opwI/AAAAAAAAA2g/kzvua7WZn1w/s800/IMGP3522.JPG

https://lh4.googleusercontent.com/-Wz-MLLzwIcY/T6cB9DM4gtI/AAAAAAAAA2s/HX4MCUaDDUA/s800/IMGP3523.JPG

https://lh3.googleusercontent.com/-uVxBetHu0Go/T6cB83_MvaI/AAAAAAAAA2o/xxB1szxEpvg/s800/IMGP3524.JPG

I know this is not DIY thread, but I will be doing some work on this and thinking of modding it. It is a little buzzy. When I get some time I'll dive in. Thanks, Keith

I can't tell you anything about your amp specifically, but in general those old transformerless amps can be very dangerous things. If you're going to use the existing electronics, add an isolation transformer and three wire power cord.

I can't tell you anything about your amp specifically, but in general those old transformerless amps can be very dangerous things. If you're going to use the existing electronics, add an isolation transformer and three wire power cord.

+1 to this.
I left a reply in your other thread in Amp Central, but If you can, try to look under the chassis and see if there are any tube makings on the chassis. The power tubes look like 50c5 to me as I had something similar in an old Danelectro amp a while back that was transformerless.
Please be safe in using this.

The skinnies are likely 35C5s. The trick with transformerless is to add up to 100. So... 2x 35 + 2x 12 = (roughly) 100.

I didn't know Garnet made those!

Not the same amp but the tremolo might be the same.

http://www.guitarscanada.com/amp-building-technical-repair/32057-garnet-stencil-tube-amp-advise.html


And a schematic for the Garnet 5P.

http://music-electronics-forum.com/attachments/8961d1271502663-5p.pdf

The skinnies are likely 35C5s. The trick with transformerless is to add up to 100. So... 2x 35 + 2x 12 = (roughly) 100.

I didn't know Garnet made those!

My gut feeling is Gar did not, I don't recall ever seeing a Garnet that ugly inside, even by true PtP standards, that is pretty ugly.

Easiest way to make is safe to play is to buy a stand alone isolation transformer to plug it into. easiest way to make it safe without having to worry someone will for get to use the iso trans is to get a 50VA triad iso trans for about $12. Mains cord to iso trans primary, iso trans secondary to full wave bridge rectifier, shunted by a 100uf cap. That feeds the B+ through the rectifier tube, to get the needed voltage there. The now DC voltage for the heaters will be to high, so change the tubes to 50C5's or 50EH5, and 20EZ7's. The existing dropping resistor should be in the ball park now. If you really worry about the heater string, remove the dropping resistor and replace it with a 150ma CCS, that way it does not matter what the heater voltages of the tubes you use are, as long as they add up to 160v or less, the CCS will automatic adjust the current to keep them operation at the right voltage

I think it was one of his stencil amps, a Piper. The above amp has the same faceplate as the one I linked to at the guitarscanada site. It looks similar in nature to the one in the middle of the stencil page.

http://www.garnetamps.com/stencil.htm

The number above the indicator light looks to be the model number, Garnet used the 5P for other 5W models and the -T for tremolo. The number under the CSA designation is the manufacturer number. I looked at some pictures of other Garnet amps and could not make out this number but I think that would be the best way to confirm Garnet as the manufacturer.

The number above the indicator light looks to be the model number, Garnet used the 5P for other 5W models and the -T for tremolo. The number under the CSA designation is the manufacturer number. I looked at some pictures of other Garnet amps and could not make out this number but I think that would be the best way to confirm Garnet as the manufacturer.

I am learning more and more here tonight. I learned about the CSA code (LR24510 indicates built by Garnet), on the Garnet web site. I located the code on my amp. It was indeed built by Garnet and was one of their stencil amps. They built amps for 30 or so different companies and put their logos on them. My model is a 5P-T.

If it were mine, I would convert it by installing a PT. Those transformerless amps are death traps

I am limited in my amp knowledge but isn't an amp running off 120V safer than an amp with stepped up voltages over 400V? I was planning to upgrade the cord ASAP.

I am limited in my amp knowledge but isn't an amp running off 120V safer than an amp with stepped up voltages over 400V? I was planning to upgrade the cord ASAP.

The basic transformerless circuit was designed for inexpensive plastic tabletop radios. The plastic case insulates the chassis. That's good because the chassis is often "hot". You don't plug your guitar into a plasitc tabletop radio.

Some low buck guitar amp manufacturers scoped the low buck circuit and saw an an opportunity to make some money.

See how it's got a tiny speaker in a big cabinet? It's styled to look "big" 'cuz bigger is better!

Back to Darwin Awards amps: The hot chassis makes your guitar hot, too. Voltage ends up on the strings. Technicians say, "You need an isolation transformer!" Musicians say, "What?" Net result is usually playin' with a hazardous condition.

I am limited in my amp knowledge but isn't an amp running off 120V safer than an amp with stepped up voltages over 400V? I was planning to upgrade the cord ASAP.


Upgrading the cord to three wire does nothing to improve safety without the iso transformer, because there is always the risk of the chassis going hot (and don't count on the circuit breaker or GFCI to protect you.)

Yes, in one sense it is not as 'bad' as high DC voltage - which hurts like hell, can leave nasty burns, and is possibly fatal.

But in another sense it is exactly like sticking a butter knife into an unprotected wall socket. AC is the kind of voltage that causes you muscles to seize up, meaning you might not be able to let go of that guitar neck until after your heart has stopped beating.

You need the iso transformer.

You can go the route Celeste recommends, but you can also wire up a dedicated iso just like an external. You just move the power switch and fuse to the primary (external) side of the transformer, attach the ground wire to the chassis, then wire up the secondary (output) of the iso to the existing power input.

Take the advice you find here, that'll be a great amp when the mods are done. If the speaker needs a change...www.loudspeakers.ca

I am limited in my amp knowledge but isn't an amp running off 120V safer than an amp with stepped up voltages over 400V? I was planning to upgrade the cord ASAP.

Worth viewing.

http://www.tdpri.com/forum/amp-central-station/324442-shorted-death-cap-vidio.html

Hello,


Okay reading all the posts I have to concur with the safety recommendation that you get an isolation transformer. Using that amp as is is like being a lint miner in a dryer fire so be safe and don't have the Angel of Death on speed dial. :)

Having said this their are two ways that this can be handled. One way is the aforementioned isolation transformer. That is probably the easiest way to do it and will give you the added knowledge that it is safer then when you got it. The other way is to take your time, examine the circuit, do some measurements, rebuild and modernize it for your tastes. You have a lot of potential here in that amp but it is up to you plus all of the changes can be undone.



Dennis

Thanks folks. I will leave the amp off and unused until I get some time to deal with it. I have no experience with an isolation transformer. I will do more research and learn about them. This is starting to sound like a fair bigger bite than I can chew. I'll just park it for now and come back to it when I finish my current 5F2A project.

See if you can find a schematic or what tubes it has. Might be able to give you some options.

That amp likely runs a 35W4 rectifier, a 50C5 power tube and the two 12A-- tubes in the preamp/driver/trem circuits. I would think that the 12AX7 is the tremolo circuit tube. This design is commonly called the 'American 5'....without the 12AX7. This is the first time I have seen one with a tremolo circuit in it. Usually they are very basic amps. They run off of the wall voltage....add those first numbers of the tubes together and you will see that voltage closely fits the wall votlage...if you add the votlage for the heater filaments in with the other numbers.
Ditto the need for an isolation tranny.

Here's a simple breakdown:

Power Transformers comprise mainly two sections. Primary voltage goes in (from the wall) secondary voltage goes out. Secondary voltage is relative to the number of turns of wire around a core. A step-down xformer produces less voltage than it takes in. A step-up transformer produces more voltage than it takes in. Tube amplifier hobbyists are most familiar with step-up transformers.

An isolation transformer's output is equal to its input voltage. What's the point of that?

Here's the key:

The two sections of a power transformer are not physically connected.

They operate according to the laws of electromagnetism.

An isolation transformer separates the guitar player from high voltage in the event of a failure in the amplifier wherein the chassis could otherwise become live.

Because in transformers, the primary and secondary voltages are separated by air space, the chassis cannot become live when an isolation transformer is in place.

Note: If a chassis becomes live, your guitar also becomes live. This can occur when a single small capacitor (affectionately known as the death cap) fails (shorts) and becomes a wire instead of a capacitor. If it fails open, you don't get electrocuted. If it fails and shorts, you do.

Good info folks. Thanks. I have decided to park the "amp of death" until I can get my job, and home building projects under control and have some time for my hobbies again. I have a 5F2A to finish, then I'll think about what to do with this Garnet amp. I am considering gutting it and building a 5F10, harvard circuit. It would be a good fit for my collection!

I have an old Pepco Trend amp and I want to put an isolation transformer. So where can i find one ????

I have an old Pepco Trend amp and I want to put an isolation transformer. So where can i find one ????
Triad N68-X at Mouser Electronics:
http://www.mouser.com/ProductDetail/Triad-Magnetics/N-68X/?qs=%252bfhPKvh1fqMgz%2fL8G7F80A%3d%3d

Under 12 bucks, and rated for 50 VA. It should be fine for a small low wattage tube amp.

I don't know about sources within Quebec - perhaps there's a local source for something similar?


-Gnobuddy