• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

How to use damper diodes correctly?

Jump to Latest
P

profun

Member
Joined 2012
#1
Recently, I have obtained some damping diodes, such as 6CL3, 17BH3, etc. They are all half wave rectifier diodes. Although they are very cheap, it seems that I rarely see works that use them in audio circuits. Can I use two 6CL3 to make a full wave rectifier circuit? Alternatively, two 6CL3 can be used instead of the expensive GZ34, which is quite interesting

image_editor_1701607420028_edit_121244692763269.jpg

image_editor_1701607395647_edit_121234094496604.jpg

ole5.jpg
 
#3
Also look at Thomas Mayer’s website vinylsavor

Plenty of examples of half wave rectifier damper diodes used in full wave, full wave bridge as well as hybrid Graetz bridges. As you state, they are inexpensive, have a slow warm up time and are useful for high voltage B+ delay. The filaments do have large current requirements that you will have to take into consideration when designing as well as not always the usual filament voltages (i.e. 5V, 6.3V, 12.6V; but 17V, like in your 17BH3, etc…). That can impact what you choose as your power transformer. They are also plentiful. They are probably rarely used in commercial circuits because you need multiples of them and many are 9 pin Novar tube bases; they should not be mixed up with Magnoval bases. They look the same except for tube pin diameter. Novar should also not be mixed up with Noval bases (small 9 pin miniature tubes like WE396A).

But since this is diy, you are free to design as you please. Goodl luck on your quest!

Best,
Anand.
 
#5
Damper diodes were designed to be used "upside-down", with the anodes tied to ground and the cathodes flying up to many kiloJolts positive. This is handy for rectifier use because the heaters can safely be referenced to ground and the cathodes at B+. Conventional rectifiers (of the same size) most often require their heaters to be referenced up near B+. We pay for that extra insulation with heater power, but that's life.

All good fortune,
Chris
 
  • Like
Reactions: dubadub, ErikdeBest and poseidonsvoice
#6
Thank you for your answers!

But I noticed that these TV damper diodes all have a common parameter "Heat positive with respect to cathode --300V MAX". This means that the maximum output anode voltage does not exceed 300V, which limits most audio circuit applications. Is there any way to solve this?

thanks!
 
#7
Yeah, no idea why that's specified, really strange and maybe important/interesting, but doesn't apply to amplifier B+ rectifier use, where the cathodes sit at B+ and heaters are at least equal or negative of that, so maybe an issue of defining the terms of the specs? Don't know, don't care (much. Puzzling, but most probably a matter of bureaucracy). Note that those voltage limits are (and could only be) specified for heaters positive to cathodes - actual operation was inherently cathodes positive to heaters. Damper diodes, anode to ground, could not have a cathode more negative (ref: heaters) than zero-ish. Why is the H-K voltage rating so different? A very interesting question.

All good fortune,
Chris
 
#8
I tried them for the first time recently, EY88 in full wave. I studied severral datasheets first, but there's not much info there on rectifier use.
I was worried about the usual max first cap value, but that doesn't seem to be an issue, I used them in front of a 390 µF cap for a while without problems. The voltage comes up rrreeeaaallll slow.
More worries about the current rating, EY88 are max 200 mA and 500 mA peak. My amp consumes 250 mA, no problem so far.
My impression is that these things can take a beating all day long. And the filaments give quite the light show!
 
#9
I've been using 6CJ3 (GE and Sylvania) in 300B-SE amps for 16+ years. They are totally reliable, and far tougher than any recent production of the historical amplifier types. They offer low voltage drop, long startup delay and 30s rise time. Perfect.

rkoonce said:
I've used them many times as slow-start devices between the rectifier and first capacitor.
Click to expand...
Yes, this is the most economical way to use them. For typical preamps, gain stages or SE amps you can simply make a bridge of UF4007 diodes, and add the damper in series with the + output of the bridge.

I prefer to use a separate split bobbin transformer for the heater, so that the cathode and heater can be connected. The voltage stress is thus placed across the bobbin, which can easily handle it.
 
  • Like
Reactions: zintolo and poseidonsvoice
#12
Do you have any comments on why currently available dual diode 5T-ish rectifiers are so bad? (Not even counting ChiCom, so really only applies to Russian or Slovakian). Why is it so difficult to make 5T rectifiers today? Those same plants make great output valves that can run at 600VDC, if not willingly, so why are 5T rectifiers so hard to do? It's a puzzlement.

All good fortune,
Chris
 
#14
Chris Hornbeck said:
if not willingly, so why are 5T rectifiers so hard to do? It's a puzzlement.
Click to expand...
Yes it is a puzzle, and a very good question - but I think that we have clues to work from.

The 6CJ3 Data Sheet begins with:

6CJ3-arcover-countermeasr.png


I suspect that the « diffusion bonding of the cathode » is one of the hard-won tricks of reliable constrution that has been lost in the transition to 1990s manufacturing. This was certainly an advance on the performance of octal rectifiers or the 1950s and earlier.

The modern production's problem is surely one of arc-overs destroying the emissive surface. The problem affects rectifiers because the stress felt by rectifiers is much heavier than for power or signal valves - especially given that DIY amp builders often don't know (or think it does not matter) about the rectifier's limitations of power-ON current allowed, and the restriction on the size of capacitors.

The fact that the dampers can withstand high voltage Vak and high current demand simultaneously, while sustaining a 30s risetime shows just how tough they are.

Lack of resilience in the cathode construction is behind another problem, I believe:
Heavy startup current imposed on half-warm power valves while the anode voltage is applied can sometimes leads to an accumulation of white powder inside the tube. This is a similar effect, that reduces the valve lifetime, but is not catastrophic and may not be noticed, given the short lifetime of some designs.

Another example: All the modern DHT builders had (at one time) problems with filament breakage at first - the Western Electric and Marconi-Osram alloy and construction secrets here have remained secret. JJ and EML addressed the problem with heavy, slow warming filament wire that is certainly not ideal.

Another:
Some modern manufacturers have not noticed, or understood why the optimal working cathode temperature of oxide coatings was usually set to occur at about 5% below the rated operatng voltage of heaters or filaments.
 
  • Thank You
Reactions: Chris Hornbeck
#15
profun said:
The application circuit of damper diodes is different from commonly used rectifier diodes, and I find it a bit difficult to understand
Click to expand...
This is the TV line output stage.

To use them in an amplifier, the peak current values need to be respected. They will work anywhere designed for GZ34, 5AR4, GZ32 GZ37, 5R4GY etc etc ... usw...

With choke-input stages, they work right up to the maximum DC current on the datasheet
 
  • Like
Reactions: Miniwatt
You must log in or register to reply here.
Top Bottom