ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 :
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

D-Clone question - lamp on back panel?


 :
10/3/2000 7:15 PM
Jim S.
D-Clone question - lamp on back panel?
Having recently purchased a pair of raw D-clone chassis from Mr. Stuckey, I realized I'd better identify what is supposed to go in each of the pre-punched holes in the back panel. So I took a look at some pictures of real Dumble ODSs.  
 
There's only one I'm not sure about -- it's the hole directly below the hole for the 50W/100W mini-toggle switch. It appears to be for a small indicator lamp of some sort. But it is not labeled on real Dumbles so I don't know what it is supposed to indicate. Does it light up when the standby switch is flipped up? Or only when the 100W setting is selected? Or does it have some other purpose? (Even better, it would be great if someone could tell me what type of lamp it is and how it is wired in.)  
 
Thanks.
 
10/3/2000 8:06 PM
Gil Ayan

Jim, that feature was discontinued by Dumble in most recent models. However, old amps had the 50/100W switch and an LED (bezel mount) indicator. As you'd have it, the LED was on when the amp was in 50W mode -- don't ask about that particular wiring because no one will tell you. Sorry. :)  
 
However, you can find an alternative way to wire the LED and have it be on in 100W mode if you so choose. Merely use a DPDT mini toggle switch for the 100/50W switch; one pole can disconnect two cathodes from ground, and the other pole energizes the LED.  
 
By the way, the indicator on the front panel is also a bezel mount LED. Modern Dumbles use LEDs, onlder ones used different neaon lights. You can buy these things from Mouser electronics, and some even have the dropping resistor included in the assembly. The easier way to power the LEDs is to build a trivial power supply from the 6.3VAC filament supply. All you need is one diode in series with a dropping resistor and you have yourself some "cycling DC" that will happily light up the LED. The dropping resistor can be anywhere between 1K and 390 ohms.  
 
Gil
 
10/3/2000 10:25 PM
Jim S.

Gil,  
 
Thank you for the info.  
 
As for using a bezel mount LED, why do you need a diode in series with the dropping resistor? Isn't this redundant, since the LED is also a diode? Sure, it will drop another half a volt, but the resistor is also dropping voltage.
 
10/4/2000 1:20 AM
Don Symes

A valid point.  
 
Consider one of those bipolar/bicolor LEDs that are a pair of diodes in reverse parallel.  
 
Do check the LED's PIV, though. That may be Gil's concern.
 
10/4/2000 3:04 AM
Gil Ayan

quote:
"A valid point.  
 
Consider one of those bipolar/bicolor LEDs that are a pair of diodes in reverse parallel.  
 
Do check the LED's PIV, though. That may be Gil's concern.  
"
 
 
Don's got it, think of the diode as insurance -- for what it's worth, the practive of the diode + LED was Dumble's idea for pilot lights, not mine. :) USed in the pilot lights for Dumbleators and modern amps alike, and of course, that part of the circuit was unpotted, so anyone can see that by merely opening an amp up.  
 
Gil
 
10/4/2000 3:36 PM
Jim S.

quote:
"...and of course, that part of the circuit was unpotted, so anyone can see that by merely opening an amp up"
 
 
So then why is there secrecy over the (I presume) trick Dumble used for wiring that 50W mode indicator LED?  
 
Just curious...
 
10/4/2000 10:03 PM
Gil Ayan

quote:
"So then why is there secrecy over the (I presume) trick Dumble used for wiring that 50W mode indicator LED?  
 
Just curious...  
"
 
 
Jim, that is a fair question, and unfortunately the answer is simply "because." If I ever bought a real Dumble, ungooped or if I tooked the goop off myself, I wouldn't mind sharing what I found with the rest of the planet [this proposition is very unlikely to ever occur; as it were, I am amp-happy for a long time to come]. However, some people just don't want information that they essentially paid for (by buying a damned amp) floating around everywhere. So, even though I don't quite agree with that position, I can definitely respect it.  
 
The LED for the light thing is no big deal, can be readily seen and is used for different "devices." The 50/100W switch is a little more interesting and I suppose that's why peole tend to be more secretive about that information. But if it helps you to sleep, in my amps, I use a DPDT switch and lift the cathode on two tubes for 50W. In 100W, I ground the cathode and connect the LED so that the little light comes on.  
 
Gil
 
   Page 1 of 2 Next> Last Page>>