Convert record player to 5E3, or custom build?

[barnett25]

Hi, I bought a portable record player to scavenge the amplifier to build a guitar amp. I had planned to build a 5E3, but now I am not sure...

The record player has two 6V6s, three 12AX7s, and a 5Y3 rectifier. This should work well for a 5E3 (either delete the 3rd preamp tube, or use it for reverb). However I am worried that the output transformer might be a bit weak at around 12 watts. Most 5E3s I have seen use 20 watt OT.

I have attached the schematic for the audio amplifier. I am curious to hear opinions on whether I should turn this into a Fender, or if there are any ideas to modify the existing circuit for guitar use?

Also, am I going to blow the OT if I use it in a 5E3 circuit?

[Stevem]

It's not the circuit it's the combo of the power supply voltage from the transformer and the amount of current the that the power transformer can put out.
With two 6v6 output tubes and that power supply voltage you will at some point fry that OT since the output stage when driven hard into the clipping that we love will be over powering that OT by at least 6 watts!
The orignal OT lasted with its 15 watt rating due to no one wanting to hear distorted records being played back!
This is the same issue Fender had with there tweed Delux amps, back in the day, they used a 15 watt OT and got away with it due to no one back than wanting the distortion that the amp could make when it was trying to pump out the 22 watts that the tubes could do!
So yes, you will need to replace the OT with a better one and after that you can ponder whatever preamp circuit you want to place before it .

[Structo]

On the other hand I installed a 15w OT in my Tweedy Dee amp because I wanted to have more saturation than the 20w OT would have.

In other words I am trying to get the amp to breakup sooner for more breakup at lower volume.

Not sure if it will handle the power but it hasn't gotten hot after an hour of playing, but I wasn't pushing it too hard.

[barnett25]

Is heat a good indicator of impending OT failure? I am wondering if I can build my amp, and just periodically check the temp of the OT to keep from killing it. If it gets hot easily, I know I need to buy a higher rated one.

Edit: It may also be worth noting that the OT I have has a 10k primary, rather than the fender stock 8k ohm. I don't know if that small change in impedance hitting the 6V6s would cause a change in the power that the amp outputs...

[Baddog01]

I've built a few amps using old phonograph amplifiers and I've never blown a output transformer. Do you have pics of the amp. Have you tried plugging into the amp the way it is? I've found that some amps sound cool right out of the box.

Keith

[rp]

Build it. So it blows up, then you get to fix it. As an amp geek you can't loose .

[Reeltarded]

I bet this one can't be blown up because it's been talked about.

[Phil_S]

Anyone else here bother to do the math from the schematic? Vk=20, Va=385, Rk=270. Ignoring the screens, I get 13.5W static plate dissipation at idle. I'm going to guess pushing this to around 18W is probably going to be OK. No guarantees, but, really, that schematic is for a hi-fi circuit with low/no distortion. A 5E3 (possibly north of 20W) might be pushing too hard or it might be fine. Build it and you'll find out. If it melts, a replacement OT won't cost an arm and a leg.

[Baddog01]

How does the size of your OP transformer compact to a Deluxe transformer. If it does run on the hot side install a fan. I did it to my Carmen Ghia clone I made using Hammond Organ transformers. She ran a little on the warm side but after installing the fan she's nice and cool. Run a 12vdc fan on 6vdc and she's fairly quiet too boot.

Keith

[barnett25]

Thanks for all the advice! Given my limited funds at the moment, I think I will do as many have advised and just try the existing OT.

Now I need to decide if I am going to try to rewire the existing chassis as a point to point 5e3, or if I am going to go ahead and build a proper Fender style chassis.

I was toying with the idea of using the record player box as the actual amp, and keep it looking mostly original. It looks like it is made of 1/2" plywood though, which may be too resonant. I am also not certain I can fit a 12" speaker in there.

[Baddog01]

Thanks for all the advice! Given my limited funds at the moment, I think I will do as many have advised and just try the existing OT.

Now I need to decide if I am going to try to rewire the existing chassis as a point to point 5e3, or if I am going to go ahead and build a proper Fender style chassis.

I was toying with the idea of using the record player box as the actual amp, and keep it looking mostly original. It looks like it is made of 1/2" plywood though, which may be too resonant. I am also not certain I can fit a 12" speaker in there.

I'd just build it point to point and call it good. Did you try the amp to see what it sounds like ?
I'd yank the record player and see if I could make a new piece of wood for that are . Cut a 12" hole in the wood for your speaker. Or you could cut the hole in the lid that opens and put some kind of grill cloth between the speaker and lid. Remove the existing speaker. Just a couple of ideas.

Keith

[barnett25]

I'd just build it point to point and call it good.

That is the way I am leaning. I think it would be cool to do it up as a combo in the existing cabinet. Use the lid as a closed back that I can open for service, or to make it an open back. The speaker would go in what would normally be the bottom of the record player. I would just need to add a frame to hold a grill cloth.

Did you try the amp to see what it sounds like ?

I did try it, but only as a hifi. It has an aux-in that I tried from my iPod. It sounded pretty good considering. However after 10 minutes of so of running well, it quickly lost volume, and got very flubby. After turning it off for a while, I tried it again, and it again played well, but only for a couple minutes this time. I assume the stock caps are to blame.

I ran it at full volume for several minutes, and neither the PT or OT got even the slightest bit warm. The 6v6s were screaming hot however.

[Baddog01]

I'd try it with my guitar before modding it. It does sound like a bad capacitor or maybe solder joint.

[Stevem]

High level fly back pulses with punch thru winding insulation in the blink of an eye and take out the OT without increasing the OTs core temp one centila!!

I have a buddy with a old mid 50s Gibson 25 watt 6l6 powered amp that when he picked it up he loved the sound , just raved about it when cranked and invited me over to hear it one day.

After listening to him play it for 3 minutes i told him something is not right with it, so we headed to my place and patched it into my test rig.

It turns out one side of the OTs primary was shorted and the amp was basically playing in Class A at low volumes and then missing half the sign wave with nasty distortion when cranked, he was very displeased with his poor ear when I pointed out what was going when viewing it on the O-scop to say the least!
Some folks ears are very easy to please when it's rapped up in a cool vintage amp that you have payed 800 bucks for!
May be I should take some of the blown OTs I have on hand and build some amps to charge killer bucks for on ebay, there must be plenty more poor ears out there with money burning a hole in there pocket! Lol!

Sent from my iPad

[rp]

May be I should take some of the blown OTs I have on hand and build some amps to charge killer bucks for on ebay, there must be plenty more poor ears out there with money burning a hole in there pocket! Lol!

Strap two trannies with half blown windings together and then say, this one's special, it's got two OTs just like the early Super Leads!