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Hoffman Amps Forum image Author Topic: Danelectro DX-250, not working  (Read 3983 times)

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Offline Jomamma

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Danelectro DX-250, not working
« on: July 09, 2014, 03:20:51 pm »
I have a Danelectro DX-250 that is not working.  Can't find information on this model.  It's a single 12" with a separate head that fits into the back of the speaker cabinet(real cool), made in Neptune City, N.J.  It has seven tubes-6X4-12AX7-7189-7189-12AX7-12AX7 and the last tube says 6FQ7 or 6CG7.  The pilot light comes on but no sound.  Any ideas where to find a schematic, and how to troubleshoot?  On a couple of the pots the whole shaft pulls out.  Would that cause the signal to stop?  I'll probably need help on how to identify and order the correct pots.

Thank you
Jomamma

Offline sluckey

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Re: Danelectro DX-250, not working
« Reply #1 on: July 09, 2014, 05:29:42 pm »
Here's a schematic that matches that tube lineup and speaker. Could be your amp. Does your speaker connect to the chassis via an 8-pin plug?

     http://el34world.com/charts/Schematics/files/danelectro/dano_dm25.pdf

Those pots could be part of the problem.


A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Jomamma

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Re: Danelectro DX-250, not working
« Reply #2 on: July 09, 2014, 07:36:52 pm »
Thank you Slukey,

I think that's the exact schematic.   The speaker connects to the chassis with a 4 pin plug. There are 9 pots on the panel- volume, bass, treble, volume, bass, treble, reverb, strength, speed.  All the pots say 1 meg. on the schematic.  Can you tell me what to order?  Should I replace the filter cap?  It's a tall silver can 5mfd, 10mfd, 20mfd.  What could I use to replace?

Thank you again
Jomamma

Offline sluckey

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Re: Danelectro DX-250, not working
« Reply #3 on: July 09, 2014, 07:53:21 pm »
Replace the broken pots. Measure the voltage on each filter cap. Measure the voltage on all tube pins. Report your findings.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline PRR

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Re: Danelectro DX-250, not working
« Reply #4 on: July 10, 2014, 12:02:57 am »
> no sound

*NO* sound at ALL? Or faint hum/hiss with no guitar? Big difference.

> On a couple of the pots the whole shaft pulls out.  Would that cause the signal to stop?

A Volume pot, turned full-down, sure should 'stop signal'. Push the shafts back in and turn the pots half-up. That should pass sound. Unless the shaft-break also shattered the internal resistor wafer. You can jumper-around this guy's Volume pots. The bass/treb pots, busted, may give odd tone but not "no sound".

> The pilot light comes on but no sound.  Any ideas where to find a schematic, and how to troubleshoot?

Car lights work but engine won't start.

Don't REALLY need a schematic to troubleshoot a car with a major problem. Some systems "just have to be" and the general symptoms don't need brand/model details.

If the car won't crank, there's a couple big wires and a little relay. You expect to find 12V a bunch of places.

If the car cranks but won't cough, you check fuel and sparks. In old days we'd pull the hose off the carb and see if gas ran out. (Don't try this on modern non-carb cars.) Also pull a spark wire and see if the sparks are happening (again, modern cars foil us; but a Neptune City DanE ain't modern.)

You want to work inside the chassis. *You can get killed in there!!* Read good tube amp safety instructions.

I would check the speaker first. Does the Ohm-Meter say 6 Ohms? If you carefully clip-lead it to your testbench amp's speaker, does sound come out? A dead speaker explains all the symptoms.

So does an un-plugged speaker. (I wonder how I know this?)

After verifying that sound could come out, I'd go for B+. Like if a car battery isn't 12V, there is A Problem. We know that tube-amps generally have B+ of 250V to 600V (so be *careful!!*). The 7189 tell me guy aimed for 400V (however the plan shows 7189 under-run at 310V, you could have run 6BQ5/EL84 in this, maybe 7189 were on-sale that month). There's a wire from the rectifier to a filter-cap (a multi-cap can in this plan). *Carefully* clip your DC volt-meter to ground and that cap. Stand back. Power-on. Watch the meter. We'd expect it to stay low while the rectifier warms up, maybe go high, then fall as the power tubes warm up. Without the plan, I'd be looking for 400V, but 310V would not be "wrong", and the plan says it is right. 100V or zero would be wrong. This points to PT, rectifier, or a short on the B+ (and if you've had it powered-up a while, you'd know if it was shorted).

The pilot light on the plan is across the 110V wall-voltage. It tells you the power switch and main fuse are good, nothing more.

PLEASE convert the power-cord to 3-pin and clip-out the ground-flip cap. When AOK, wrong flip gives a strong tingle which you probably survive. When 50 years old, that cap could be dead-short and flow "infinite" current through you to ground.

Offline Jomamma

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Re: Danelectro DX-250, not working
« Reply #5 on: July 10, 2014, 09:13:16 am »
I found a burnt resistor (27k I think) off of pin 1 on the tube marked 6FQ7 or 6CG7.  The tube that is the socket is a 6V4.  Is that okay?

I'm having fun now!!
thanks

Jomamma

Offline Willabe

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Re: Danelectro DX-250, not working
« Reply #6 on: July 10, 2014, 09:36:42 am »
I found a burnt resistor (27k I think) off of pin 1 on the tube marked 6FQ7 or 6CG7.  The tube that is the socket is a 6V4.  Is that okay?

Well a burnt plate R is bad.

My GE tube manual says 6V4 is a 9 pin full wave high vacuum rectifier. It can NOT be used as a substitute for 6FQ7/6CG7 which is a medium mu dual triode. The 2 are completely different animals.

It's the reverb driver tube. You can just pull that tube out and see if that helps, it won't hurt anything. You just won't have reverb. Looks like only channel 2 has reverb. Then;

Get a hold of the correct tube and change the plate R. Also check the other triodes plate R.


               Brad     
« Last Edit: July 10, 2014, 10:16:57 am by Willabe »

Offline Willabe

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Re: Danelectro DX-250, not working
« Reply #7 on: July 10, 2014, 09:57:25 am »
PLEASE convert the power-cord to 3-pin and clip-out the ground-flip cap. When AOK, wrong flip gives a strong tingle which you probably survive. When 50 years old, that cap could be dead-short and flow "infinite" current through you to ground.

(To be clear, "flow "infinite" current through you to ground" = death.)

Please do this 1st!

Here's a drawing with the 'death cap' out lined in red, snip it out before you work on the amp any more! Then add a proper 3 wire power cord, our host Doug sells them in his on line store. This is a MUST do!

http://hoffmanamps.com/MyStore/catalog/parts14.htm


                          Brad    :icon_biggrin:
« Last Edit: July 10, 2014, 10:03:30 am by Willabe »

Offline Jomamma

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Re: Danelectro DX-250, not working
« Reply #8 on: July 10, 2014, 12:06:32 pm »
Thank you for the death cap info. I'm guessing it's the orange drop in the photo (see attachment), never mind the attachment it took too much space, couldn't figure out how to reduce.  I remove the cap, install new cord, put ground to transformer bolt?  What about old power switch that allows for polarity, do I leave that in there? 

The wrong tube explains burnt resistors around tube socket.  The amp will work without the 6FQ7?

You guys are great
Thank you
Jomamma

Offline Willabe

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Re: Danelectro DX-250, not working
« Reply #9 on: July 10, 2014, 12:32:54 pm »
I remove the cap, install new cord, put ground to transformer bolt?

Yes, that would be fine or you can use a separate chassis bolt with good star washers to bite/cut into the chassis for the ground.

What about old power switch that allows for polarity, do I leave that in there?


Yes that'll be fine.

The amp will work without the 6FQ7?

Yes I think it will but you'll have no reverb.


                  Brad     :icon_biggrin:


Offline Willabe

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Re: Danelectro DX-250, not working
« Reply #10 on: July 10, 2014, 12:37:12 pm »
I'm guessing it's the orange drop in the photo (see attachment), never mind the attachment it took too much space, couldn't figure out how to reduce. 

Here read this, it should help you.

http://el34world.com/Forum/index.php?topic=464.0


             Brad     :icon_biggrin:

 


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