Help! I tried to recap my amp!

[Aurora]

Aha - of course - Agreed on the strain relief.....ideally there should be an IEC socket, but that's a major PITA to install in an old amp, without proper tooling.....
I'l have look in my catalogues for another solution......

[Phil_S]

would this thing work?DocZ

+1 on that Grundig is too nice to butcher for a guitar amp. If you are not otherwise emotionally attached to it, sell it on eBay. You will get a very good price for it and should be able to take what you get for guitar amp parts.

[docz]

The strain relief is just temporary, I am going to install a IEC connector once I get this all up and running, so that power cable is just there for the testing/troubleshooting phase.

I just got a Dremel type tool, and I made a new hole, I couldn't find any solder lugs at the store, so I used a screw and a computer mainboard turret - being a computer technician the last 15 years I have tons of stuff like that laying around. I also put some loctite there like you said. Then I soldered the mains ground wire to that turret and I soldered the artificial CT to one the PT's chassis bolts.

I changed the .022uF leaky cap with the old "death cap" they had the same value, but the "death cap" had 1000WV instead of 400WV.

Results, new cap is not leaky, I got 0V DC from it. Sound is a bit clearer now, it is hard to describe, it just sounds a bit cleaner. Hum just present when I am not touching the guitar or the guitar is extremely close to the amp, low pitched hum is completely gone. I was really optimistic this time. Everything worked great, tremolo, reverb, tone, volume, no scratching, no distortion, no static. Then after about 15 minutes there was a faint frying pan static, then it got louder and louder, then the tremolo died, and noise was dominant. So I got my chopstick out and started poking about. Poking the .01 uF coupling cap on V1 gave a big pop that cured the static for a little while, then it returned. I can not find any DC coming out of this coupling cap though...

DocZ

[docz]

The radio was not mine, it was just something I found on the Norwegian equivalent of craigslist

I have no idea what voltages or circuits are involved, except that it said it had tubes, but I do not know what kind. It was dated 1952.

It was the cheapest I found, so I thought it would be a nice donor. But I'll look for something else since this is worth saving.

Here are a few more I found:



[img:575:431]http://cache.finn.no/mmo/1/200/688/91_1951068869.jpg[/img]
[img:575:431]http://cache.finn.no/mmo/1/200/688/91_-2055280718.jpg[/img]
[img:575:431]http://cache.finn.no/mmo/1/200/688/91_1186719110.jpg[/img]
[img:575:431]http://cache.finn.no/mmo/2/200/910/02_-756530163.jpg[/img]
This one is huge! I think I can build a 4x10 combo out of this!

[img:575:431]http://cache.finn.no/mmo/1/203/942/81_1287182458.jpg[/img]
This one says "EL84" or "EL34" on the back, maybe that is a good candidate?

DocZ

[Aurora]

Are these last pic's stuff you have or found locally?
Is that last Milano one a "Blaupunkt"? The badge is too small....??

[docz]

It is not stuff I have, I have found them for sale. The last one is a Blaupunkt Milano.

DocZ

[Aurora]

Not sure if it's worthwile moneywise..........
I found no free schematic... "Norsk radiohistorisk forening" will charge you 9 kr pr page, plus a members fee.......plus the cost of the radio...? And you really need that schematic to pull some important info....

A 5-10W transformer set will set you back some 8-900 kr - plus all the other gadgets you need. If you decide to go for it, and the radio is still working, you can wire it to your guitar through the "Gram" input with banana plugs, at least for testing This was a typical setup in the 50's, when amps were even more scarce than money around here....

I actually remember my father's dance band from the late 50s using stuff like this......
BTW - given your location, find an old "Vingtor"... from Horten!

[docz]

Would this thing work?

[img:200:176]https://www1.elfa.se/data1/wwwroot/webr ... df5d02.jpg[/img]

It has a secondary of 315-0-315 and 12V.

It costs about 60$ so it is about the same price as those old radios.

DocZ

[Phil_S]

...I soldered the mains ground wire to that turret and I soldered the artificial CT to one the PT's chassis bolts.

I changed the .022uF leaky cap ....

Results, new cap is not leaky, I got 0V DC from it. Sound is a bit clearer...low pitched hum is completely gone...Everything worked great...

Then after about 15 minutes there was a faint frying pan static, then it got louder and louder, then the tremolo died, and noise was dominant. So I got my chopstick out and started poking about. Poking the .01 uF coupling cap on V1 gave a big pop that cured the static for a little while, then it returned. I can not find any DC coming out of this coupling cap though..

DocZ

It sounds to me like you are almost done with it. Change that .01 cap. It fails the chopstick test, DC or no DC. Again, anything close in value is OK.

It is normal for an amp to amplify pickup induced hum when the guitar is plugged in. That isn't part of the problem.

Great work Doc. You should feel really good about this. This amp wasn't an easy one to fix, especially for a first timer. Congratulations.

Phil

[Aurora]

What's the current rating on that?

BTW - that Motron guy up at Vestfossen I told you about, sells Hammond transformers. A 5-8 W SE transformer from th e 125 series is about 400 kr...Power transformers are 6-800 kr...

This guy also sells some interesting kits that looks good....
no idea if they're better or worse that what several other posters here offer, but somehow it's easier for us to get stuff from England..less postage
http://www.ampmaker.com/

[docz]

0.024 and 1A

DocZ

[docz]

Thanks Phil, I hope that cap is the culprit! I've just ordered a replacement, so I hope it will be ok after that.

DocZ

[docz]

ok, found a cap, changed it, now the tremolo works again. (It could be that the tremolo just had a good moment, like the last time I thought I had "fixed" it, but I'm staying positive ) Noise is still there, but considerably lower. Seems the other coupling cap on V1 gives the same pop when I tap it with my chopstick, but this pop is "reverby". Also pushing the terminal strip that connects to most of the output tube stuff still seems to excite the noise - but not so much as before the newest cap change. I think I am zeroing in on the problem. Now I just need to get more coupling caps.

I do have a .022 disc cap, I do not know it's working voltage though, it is not printed on it, but it is pretty large in size, about 10 - 12mm in diameter. Will that work? At least for a test?

DocZ

[Phil_S]

Those ceramic disc caps are often 600v or 1000V. Got a picture?

Several messages back, I think Aurora posted about the difficulties of making a hole for an IEC inlet. This is not so hard. You'll have to translate from SAE measure to metric, though. Drill a .75" (19mm?) hole. (Multiple smaller holes are OK, too, but this is the least amount of work.) This is the short dimension on the IEC rectangle. Use a mill file to make it square and to remove enough material for the 1" (25 or 26mm) side. It will take you about 30 minutes and anyone who is home with you will complain about the noise you make with the file. This is not for production type work, but for just one, it is cheap and it works. You can file out the rectangle to be exactly the right size.

After you drill the hole, but before you file, use masking tape to define the rectangle. It will save you time from measuring over and over.

Look at the first picture. That rectangle was made as I describe it. This is a steel chassis. In aluminum, it only takes about 15 minutes.
http://home.comcast.net/~psymonds/TMB18W.htm

[docz]

Wov that looked good! I honestly can't wait till I get my hands on a new project, but I will fix this old thing first! I'm guessing with some practice I can make that hole with my new Dremel. The question is where is there room for that connection...

Maybe I can just file the existing hole that the power cord is using now? It is about 15mm in diameter.

Here is a picture of the disc cap, I used it for an experiment, I tried to build an electret microphone, if it worked out good I was going to try to make a headset mic out of it and use it for my gigs. My initial idea was to make it powered by phantom power, but that circuit needed a lot of stuff I don't have, transistors and zener diodes and stuff.. So I followed a simple tutorial hooking it up to a 9V battery. It turned out pretty good, a bit trebly, but very low noise, except when I moved or taped the electret. So I thought I'd see what happened if I changed the cap value from 10uF to .022uF and I put in this little bugger. I thought it would do something to the frequency filter, but it actually just made it more quiet. Oh well... enough about that I'm digressing - I'm quite good at that

Here are the pictures: