Danelectro DM-25

[Structo]

I recently had this amp sent to me to recap and install a three prong cord and to fix whatever else was wrong.

Point to point in a small chassis = pain in the arse to work on.

It had a 20-20-5 uF cap can which was a pretty small diameter can.
AES had one that was sort of close but too tall and they wanted $36 for it!
I ended up getting a JJ 40-20-20-20 can which is a shorter fat can.
I was a little worried that the larger rating would screw with the tremolo a bit but it works fine and is very quiet.

The standby switch on these is kind of weird in that it just connects the two grids to the power tubes together.
That switch was toast and did not close. So I replaced that.

This amp originally used 7189 power tubes which are hard to come by and expensive at $32-40 each.
EL84's work fine as a substitute. THe 7189 just has a higher plate voltage rating, both are 12 w tubes.
The voltage was low enough for the 84's to work fine.

Funny thing is that it runs all the heaters from the 5v winding.
Since modern voltage is higher now, it comes up to close to 6v.

Neat little amp with a lot of grind when dimed.
Has Tremolo and Reverb. Trem works fine but the Reverb is the piezo type transducer and sounds very sprongy if turned up much.

This amp is a piggyback style amp in that the amp fits into the back of the speaker cab for easy transport.
I wish it was mine.

[IMG:443:500]http://i23.photobucket.com/albums/b392/ ... iw5_ss.jpg[/img]
[IMG:399:500]http://i23.photobucket.com/albums/b392/ ... a5z_ss.jpg[/img]
[IMG:768:576]http://i23.photobucket.com/albums/b392/ ... dano25.jpg[/img]
[IMG:800:535]http://i23.photobucket.com/albums/b392/ ... EE0224.jpg[/img]
[IMG:800:535]http://i23.photobucket.com/albums/b392/ ... EE0221.jpg[/img]
[IMG:600:344]http://i23.photobucket.com/albums/b392/ ... mxb_so.jpg[/img]

After the work. Hard to tell what I did.
The Carling switch I had on hand to replace the Standby with is a short bat switch. The two 25uF bypass caps are on the second and third tube from the right.
I hope the guy doesn't mind, I wasn't going order just a switch.

[IMG:797:328]http://i23.photobucket.com/albums/b392/ ... G_0607.jpg[/img]

[xtian]

That's REALLY interesting. Thanks for the photos! So that long bar is the reverb?

[Structo]

Yes that is the reverb "tank".
It sits on a couple leaf springs.
Uses piezo transducers but does have a spring inside.

It is a very short reverb in that if you turn it too high it sounds bad.
But for a cool surf vibe it works when turned way down.

I'm not sure of the condition of the 6FQ7 tube which is what it uses on the reverb channel, but it works.

The rectifier tube on this thing is a little 6X4 7 pin.

I was a bit worried about that one but it seems to work fine.

The Vibrato or Tremolo uses a 12AX7 and uses a "bug" consisting of a photocell and a neon bulb (I think).
They are both encapsulated in an aluminum tube.

[Sonny ReVerb]

Very cool, Tom. It's interesting to look inside these old 'bargain' amps. Thanks for sharing.

[Phil_S]

I'm going to suggest the trem octocoupler uses an incandescent bulb. Cool amp and pix. Thanks.

[Structo]

You could be right Phil but when I checked for resistance on the bulb, I got nothing.

On the schematic it shows a lamp symbol with a dot on one side and I thought that denoted a neon.

[Phil_S]

On the schematic it shows a lamp symbol with a dot on one side and I thought that denoted a neon.

Yeah. Maybe it's not right to generalize, but, based on my experience with Gibson schematics from that era, I'm going out on a limb to say the they didn't pay close attention to using the correct symbol, particularly for this sort of part. I remember posting about the one in my GA20-RVT to a group of electronics guys. (The reason for posting was that I needed one and it was made of unobtanium.) Because of the schematic, the pocket protector crowd bothered to argue about whether the thing was neon or incandescent. I tried, as hard as I could without ticking them off, to tell them that such an argument was specious, as I was 100% sure it was incandescent. IMO, there's a 50/50 chance yours is, too. That dot could be "dirt".

[Structo]

You may be right Phil.

Although, like I said, I didn't get a resistance on it like you would with an incandescent bulb.

Only after it was powered on did I get any type of reading on it which was the voltage drop.

I'm not even sure if a neon bulb would respond fast enough for it to work for the wiggler.

Anyway, I crossed my fingers that it would work because there was no way I could find another 'bug' or even try to replace the bulb inside because of aging and brittle parts.

[RevD]

I'm pretty sure this amp is one of the models that Danelectro built for Sears as well (sold under the silvertone label). The head tucked into the speaker cab is sort of a give a way same as the silvertone ones. They're pretty cool little amps and your right do have good grind to them.

Regards,

RD

[selloutrr]

great amp!

They have made a very strong come back in the last 10 years thanks to bands like the white stripes and weizer.

the sears/silvertone/danelectro amps record very nicely with a ribbon mic and single coil pickup.

thanks for the post!

[mlannoo]

Thanks for posting this thread - I'm a little late to the discussion though.

I just picked up a DM-25 and have a couple questions. I understand this is a "fixed bias" amp? If that's the case, on the schematic is the bias supply filter cap the 10uF/450v inside the capcan? Which resistor sets the bias? I'm unsure how to correctly bias this particular amp.

Secondly, what is the wattage of the Jensen speaker that came with this amp?

And lastly - What common things should be replaced if I decide to do an "overhaul" on this amp? 3 prong grounded cord, the 3 filter caps (inside the cap can), new power tubes /bias, bypass caps, clean pots/sockets ... am I missing anything?

Btw ... this is my new favorite amp. I've recorded with one of these several times the past few years using my friends ... and now I have one of my own!

Thanks
M

[Structo]

This amp is cathode biased but it is also affected by the tremolo output.

The 100 ohm 5 watt resistor on the cathode is the main bias resistor.
There is no cathode bypass cap on the power tubes.

I'm not sure about the speaker as the guy only shipped the head to me.

So the modifications are:
Install three prong cord.
Disconnect the ground switch and death cap.
Replace the Cap Can filter. I used a JJ 20uF, 20uF, 40uF multi-section cap
Replace the 25uf cathode bypass caps on the preamp tubes.

Don't forget the can clamp for the cap can.

[dreric]

I have one of these, cool little amps. The stock speaker was a Jensen CN12 on mine. The DM series was late in the history of Danelectro and they were sold via music stores where as the Sears stuff was re branded "silvertone". I'd have to look it up but the DM series may have been made by MCA after they bought out Dano. These were also sold under the name Coral.

Careful, some use 7189A which are not the same tubes as EL84 / 7189

I like the old Dano stuff if only as a reminder that consumers were one intelligent enough not to touch an exposed lead and ethical enough not to sue if they did.

Eric

[Structo]

Schematic

[Firestorm]

One other thing that's goofy/neat about these is that the reverb is a separate circuit from the preamp so you can play just the reverb (i.e., no dry signal). Great if you're scoring a 1960's sci-fi pic