A couple questions regarding an amp I am converting

[Slunderfungus]

I am converting an old audio amplifier from a jukebox to a guitar amp. It came without an OT so along with tubes, and replacing the inputs and speaker terminals with 1/4" jacks I have had to find an OT. I aquired a Thordarson 4131(it came free) butits about as old as this amplifier is(50s,60s) but cannot get a reply from Thordarson as to whether or not it really is an OT and if so what the specs are.




Sorry its so big

I also wants some insight into octal preamp tubes. It is currently wired for a 6SC7,6SL7, and a6SN7. It is a Rauland 1810 with three channels, the first channel or MAG uses the whole 6SC7, and half of the 6SL7. The second channel or CRYSTAL uses the other half of the 6SC7, the AUX uses half of the 6SN7,,then the other half drives the 2x6V6 power tubes. On the off chance I want it a bit more aggressive how hard would it be to wirethe 6SC7 position to run the 6SQ7? I have decided that I want to keep it running the octal preamp tubes instead of buying the adapters to run 12ax7. I figure that later on I might be able use the other channels to either run tremolo or reverb. for right now I just want to get it running, and then look into giving it teeth.

[phsyconoodler]

The transformer in the picture is a power transformer.It has all the wires needed to hook up to a rectifier with a centre tap and the greens are filament wires.The black wires hook up to the AC power source.
Keep looking for an OT.

[TweeDLX]

Go here:
http://www.musicalpowersupplies.com/index.html
Matt is very helpful, and will answer your questions promptly. His prices are super low. I bought a 40 watt OT for $29. It's not a Mercury Magnetics, but it works just fine.

Mike

[Slunderfungus]

Thanks, I will check them out. I'm really wanting to get this amp done and play it.

[M Fowler]

Just get a Weber OT 4k primary 40w rating 4/8 ohm secondary. Anything rom 4k to 5.2k primary will work fine or Deluxe rated OT.

Mark

[Tone_Terrific]

FWIW-
MAG=magnetic cartridge input i.e. high gain
CRYSTAL= crystal cartridge (much higher output)
AUX= line level, more or less.

Mag should be plenty for guitar but if you are looking forward to 'great' tone be prepared for mediocre results. If you are just doing a project for the experience, good luck.

[donnyjaguar]

I'd convert to all 6SN7 tubes myself. These are more common and you have enough of them to get the gain you'll want.

Guessing there is relatively low voltage on the output tubes because of where it came from. Makes for great overdriven tone but don't expect a lot of power.

[Slunderfungus]

The 6SN7 tubes are have an amplification factor of 20 compared to the 70AF the 6SC7 and SSL7. I am looking to the possibility of just running all the tubes through a single channel for the possibility of a decent amount of gain for hard rock.I don't ned it to do clean, I have two amps that already do that quite well for the few and far between occassions I use it.

I have found and bought a Mercury Magnetics OT, and ofcourse another dearly needed item for those of us who dabble into this kind of stuff...a variac. I bought the variac strictly to use for its intended purpose not for that "brown sound" I have no interest in damaging any of my amps...I'm not rich enough to try stuff like that. Then again for all the respect I have for EVH and his earlier tone, the brown sound is just not my cup of tea. TBH I can get close to that sound using a Behringer TubeMonster and a Crate Vintage Club 5212 loaded with Swamp Thangs running said Tube Monster with the mids and gain dimed, on the lead channel of the Crate with its gainset on 2 oclock...atleast at living room volume levels. Ofcourse that could change as an increas in volume takes place but for now I'm only playing at living room levels

[Slunderfungus]

Originally Posted by Tone_Terrific

FWIW-
MAG=magnetic cartridge input i.e. high gain
CRYSTAL= crystal cartridge (much higher output)
AUX= line level, more or less.

Mag should be plenty for guitar but if you are looking forward to 'great' tone be prepared for mediocre results. If you are just doing a project for the experience, good luck.

The project is for the experience but I don't get why the tone should suck so bad. Its basically running the same compnents you'd find on any vintage Fender Amp.

Originally Posted by donnyjaguar

I'd convert to all 6SN7 tubes myself. These are more common and you have enough of them to get the gain you'll want.

Guessing there is relatively low voltage on the output tubes because of where it came from. Makes for great overdriven tone but don't expect a lot of power.

To a point as per the tubes. You can get 6SL7s from Tungsol as new issue, in fact I bought two, The 6SC7 are easy enough to find on fleabay, its finding them in a glass tube that can be a trick...same thing with the 6SQ7, I found a glass tube in the latter for $5 shipped and snatched it up, It is an RCA NOS and further inspection shows it too is a Tungsol. Tungsol etches an octagon withthe tube type inside the octagon.Even though its not wired for the 6SQ7 If I find a need for more gain I will look into rewiring it to take one or two.

The power trannie is easily as big as both of my 50 watt amps...in fact I think its bigger than the Vintage Club's. According to the photofact sheet I got for it the PT is delivering 335VAC to the rectifier, The specs of the PT on the photofact parts list are:
Pri: 117VAC
Sec 1: 670VCT .085ACD
Sec 2: 5VAC@2A
Sec 3: 6.3VAC@3.1A

[mark norwine]

Originally Posted by Slunderfungus

The power trannie is easily as big as both of my 50 watt amps...in fact I think its bigger than the Vintage Club's.

According to the photofact sheet I got for it the PT is delivering 335VAC to the rectifier, The specs of the PT on the photofact parts list are:
Pri: 117VAC
Sec 1: 670VCT .085ACD
Sec 2: 5VAC@2A
Sec 3: 6.3VAC@3.1A

Those specs are not all that big. This unit may be physically large, but IMO those numbers will not come anywhere near making a 50W amp.

The HT winding is only 85mA.....think about it: that's a pair of 6L6's @ 40mA each. That's a smidge more than idling.

Personally, to make an amp of any meaningful power, I'd want a PT to deliver at the very least around 150mA.

If you only want to make a small-power amp, you can find smaller iron that will do the same job.

[Slunderfungus]

Oh, I must apologize, I had thought I had also added the power tube and rectifier tube types. It is a 2x6V6 and is rectified by a 5Y3. Which is the biggest reason I bought this one. I was looking to build a 6V6 amp from scratch when I found this one for cheap. I'm only looking to get 15-20 watts max. Its all I've wanted in the first place for this project.

I did know it was on the low side, and am prepared to replace it for a more powerful tranny should it not put out thewatts I want. That said, the whole purpose of this project in the first place has been to have a 15-20 watt amp, and to learn more about amps in the process. Well that and to justify it to the wife.