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Channel 2 not working, 50s Danelectro

RodR

Member
Messages
680
Hi! After lurking these forums for some time, I finally registered and this is my first thread. I have an issue with an old Danelectro amp, it is a Special Series D Model 68. It has two channels with two inputs each, channel 1 works fine on both inputs, but channel two is completely dead. No noise or hum or anything when using any input or moving the volume and tone pots for that channel. It has the original tubes and they are working find, I tested them in another amp, so I don't think it's a tube issue. I measured the pots with a Digital Multimeter and they seem to work fine. Measured the resistance value on the first resistors on the input jacks, and both measure about the same.

Amp is completely stock as far as I can tell, I did update the original two prong power cord to a three prong and removed the death cap. Original tubes, caps, resistors, transformers, and both channel one and tremolo work without any issue so far. Any advice on what could be wrong here? I will reply with pics. Thanks for reading!
 

RodR

Member
Messages
680
The Dano





TOP two inputs and pots are for the non working channel




Closer



I appreciate any help!
 

Kyle B

Silver Supporting Member
Messages
5,123
Don't supposed you've found a schematic???

No? I didn't think so....

Did you do the chopstick test yet????? Could be simple as a bad solder connection.

It's a decent chance that Channel 1 & Channel 2 are basically wired the same. So pull out your ohmmeter and start taking some readings. See if you can find what's different.

BTW - this amp desperately needs a cap job. I wouldn't plug it in again until all those old EL's are replaced.

My guess is that the problem is one of the yellow caps that are buried under all that circuitry. Why? Do I suspect those caps are weak? No. It's because a side effect of Murphy's Law is that the most likely failed component is the one that's hardest to get at

if you can't find a schematic, you might consider attempting to draw your own. The circuit isn't THAT complex - You can probably do it in a couple hours.

Personally I wouldn't even be messing with it w/o a schematic. Some of the guys on this board have seen enough amp they might be able to work on it w/o one. But to me, trying to work on an amp w/o a schematic is like trying to drive to Florida w/o a map. Yes, you can keep going south and maybe eventually get there, but you'll end up in alotta wrong places first.
 

Blue Strat

Member
Messages
30,322
For anyone who's curious, THAT's a point to point amp...not that there's anything especially GOOD about that. ;) Especially when it's time to replace a component and you end up having to replace 8.
 

RodR

Member
Messages
680
Thanks Kyle! You are right, I did not find a schematic for this amp. I don't know what you mean by the chopstick test (sorry, I'm mexican and not familiar with that term).

There are some subtle differences in the wiring on both channels, but it sounds like a good idea to compare readings on what is similar on both of those channels.

I did not wanna mess with the caps yet since the other channel is working fine with no noise or other issues, and I do not have a lot of spare time right now. The guy I got it from said he rarely used this amp for the past 30 years or so.

I agree with you on the schematic, I think I should draw my own, I am an engineer with some background on electronics, so I should be able to do it.

In case of replacing caps, would you recommend a full recap?? thanks again!
 

Kyle B

Silver Supporting Member
Messages
5,123
I don't know what you mean by the chopstick test
Poke everything with a wooden stick while it's running - see if you can find something that you jiggle and makes it work. NOT A PENCIL (Prob not a great idea to use a stick with conductive graphite running down the middle)

The guy I got it from said he rarely used this amp for the past 30 years or so.
Totally irrelevant how often it's been used. EL caps dry out over time. Actually, the situation is WORSE if they've not been used as they degrade faster if DC voltage is never applied to 'em.

Let's put it this way.... An EL cap is nothing more than two long strips of aluminum foil separated by slightly damp tissue paper all rolled up in a nice little tube. Firing up that amp means you are putting 500V across a 50 year old piece of tissue paper. As an engineer, hope you can see the folly in that ;)

Although it can be fun when one explodes. Looks quite alot like Times Square on NYE

I agree with you on the schematic, I think I should draw my own, I am an engineer with some background on electronics, so I should be able to do it.
You surely should be able to! It's nothing compared to solving a 4th order differential equation LOL

In case of replacing caps, would you recommend a full recap?? thanks again!
Only the electrolytics (for now). The other caps are where the mojo comes from :)
 

RodR

Member
Messages
680
I did look for loose or unsolder components, but not while it was running, might be worth to try that chopstick method. I have seen caps explode more than once back in school, really smelly stuff. I once had a piece of a chip hit me in the forehead when it exploded!:p

If I have the time, I will try with the chopstick method tomorrow. If that's not working, I'll have to wait til I get some free time and find some decent caps around here to replace them. Thanks
 

RodR

Member
Messages
680
one more question, excuse me if I sound stupid but I want to keep learning. I am not very familiar with old caps, I only worked with the newer electrolytics that are really easy to spot, but I am unsure which ones would be the electrolytics in this circuit. I think the red planets and the one that looks like a planet but smaller and kinda orange, but I am unsure about the rest. Am I missing something? completely off?

Also, should I look for something in the new replacement caps? Or as long as they are EL and the values match everything is fine?
 

Kyle B

Silver Supporting Member
Messages
5,123
Every cap with a "+" on it is surely EL.

After you sketch out the circuit, scan & post it and the EL caps can be easily identified by somebody here. This circuit is almost certainly nothing "special" --- It'll follow more-or-less some common principals.

For new ones - Yes, basically you match the voltage rating, capacitance and physical form factor. There's obviously more that can be spec'd than that, but those are the 3 key parameters you have to meet. You can go higher on the voltage rating, but keep capacitance close as possible
 

Blue Strat

Member
Messages
30,322
One easy thing you can try, which is often fruitful, is cleaning all the tube pins and sockets. All it takes is ONE pin not making a good connection and the channel won't work.

Get some electronic spray cleaner (Radio Shack, Home Depot, Lowes) and spray the tube pins, and slide it in and out of the socket a few times. You'd be amazed at how often this works.

Short of this, with no schematic, test equipment, or understanding of electronics...it'll be a tough road.
 

RodR

Member
Messages
680
So all of them? I say this because I can see the band indicating polarity on pretty much every cap, excuse me if I am being dumb :rotflmao
 

RodR

Member
Messages
680
Thanks Blues Strat, I will try cleaning the tube pins and sockets. Did not know one pin could take out the channel.

You are right, I don't have an exact schem, I plan on drawing it myself hopefully soon. As for test equipment, I only have a cheap digital equipment. And about electronics, I do have some understanding, and have built some simple circuits, I don't have any experience working on amps other than replacing the two prong cord. But I want to learn, seeing as there is few amp techs in my city, and I don't know if they are any good working on this kind of amps, might as well try and do it myself and learn. Thanks for all your advice!
 

Kyle B

Silver Supporting Member
Messages
5,123
Did not know one pin could take out the channel.
The funny thing about electronics is that, unlike mechanical stuff, it only takes 1 problem to bring a whole system down. If your wheel is missing a lugnut - Eh, it'll be ok, you can still drive. But pull any resistor out of a circuit and you're sunk

You've already learned how to discharge the caps before sticking your fingers in there RIGHT? They'll hold a charge long after power is removed, enough to REALLY hurt you.

Pretty much every cap with some sort of polarity mark is gonna be an electrolytic. Sorry :) Yes, there will be several.

if you're not sure, post a picture of the ones in question
 

RodR

Member
Messages
680
I know, a single resistor could bring the whole thing down. I had more of the idea that if a pin on a tube was bad or not making good contact, It would bring all channels down, not just one, that's what seemed odd to me, but then I think channels can share the same tube, so some pins affect one channel and some the other.

That's right Kyle, I already know how to discharge the caps and test for voltage on them with the multimeter before working on the amp.

And yes, all of the caps have either a band or the "+" sign on them, you can see them all in the pictures above, so I might have to replace all of them :jo

Hopefully is just a really dirty tube socket, because I already tried different tubes (power and preamp that I know work fine), that way at least I know I have a fully working amp, and the recap will be more maintenance than hoping to fix my problem.
 

zenas

Member
Messages
8,873
That amp has Astron coupling caps the yellowish ones with the band on one side. Those could be bad but I wouldn't change them unless they are bad.

The electrolytics on the other hand? I would change all of them. They'll have values like 8uf and up. With voltage ratings from 25ish to 450ish volts. And almost always have a + and - on them because they need to go in the right way ONLY.

The "bands" on the coupling caps mark the outside foil. You can put them in either way and they'll work and not blow up like an E cap.

If it was me I'd do all the E-caps, clean all the contacts and pots, install a grounded cord (and fuse if it dosen't have one) and pull the death cap. (keep the death cap because you may be able to use it as a coupling cap)

That's a quick and dirty service on a vintage amp. Blackface Fender that's all you need 99.99999% of the time.

This ain't a BF Fender though so it may have a bad coupling cap. How do you tell ? Do the service and try it. If it works your done.

A schematic is nice BUT if nobodys screwed around in there and moved **** all you need to do is replace parts one at a time EXACTLY the way they are now.

Those old point to point amps are a Royal bitch to piece back together when some idiots been in there messing around. I just finished an early 50s Newcomb PA that thankfully had a schematic inside because some idiot "fixed" it. (fixed it for the landfill)

My "reward" for getting that rat's nest working? A 47 Kay that someone tried replacing a 6J7 tube with a transister and then cut all the wires going to the fielcoil speaker. No schematic for that one!

Your amps going to be a breeze compared to those two !
 

Blue Strat

Member
Messages
30,322
I know, a single resistor could bring the whole thing down. I had more of the idea that if a pin on a tube was bad or not making good contact, It would bring all channels down, not just one, that's what seemed odd to me, but then I think channels can share the same tube, so some pins affect one channel and some the other.
Oh yeah, it depends on the circuit and where the tube is in the circuit. You can definitely take a whole amp offline with one bad tube pin connection.
 

RodR

Member
Messages
680
Thanks Zenas, if that's the case then it is a lot easier, there is only 3 caps with + sign on them, the rest have the band. I was confused because the many including the astrons don't look like EL caps, but have that band that I thought indicated polarity.

I already replaced the two prong power cord with a three prong, and was able to reuse the original strain relief. I removed and saved what I think is the death cap, is the cap you can see in the lower part of the picture where the whole circuit is showing. It used to go from the power switch to the ground on the input jack for the tremolo footswitch. Is that correct? I have turned it on after replacing the power cord and works fine (except for the dead channel 2)
 

zenas

Member
Messages
8,873
Yeah the "death cap" goes from ac to ground. It's called a death cap because if it shorts it puts wall voltage on the chassis depending on how the original two prong plug is stuck in the outlet.

Looks like atleast one of those E-caps is a multi cap. Nothing more than two caps inside one paper tube.
 

RodR

Member
Messages
680
Yes I noticed that, the question is, how would you replace that? get a new cap for each of two leads and wire them in parallel? or both leads to just one new cap?

Also, does it matter the quality of the caps? I think it's no going to be easy for me to get good quality caps where I live...
 




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