Dynaco St-70 Running On a 83 Murcury Vapor Recitifer!!

[zastin17]

Now why did I do this?

Is it for better sound? No absolutely not.

Is it because i'ts beautiful and dangerous and wacky? Yea, probably!!!

I made an adapter with a socket saver and 4Pin socket just soldering through the pins. 3A filament, very close to 5U4, but far better in voltage drop.

If I am to ever use this 83 on the ST-70, it needs to be preheated. And during power on, I need to bring the amp up slowly up to the point where the cathode begins to conduct, before going higher. So slowly bring the amp up while the 83 is already hot on a Variac, watch until the fillament begins to conduct, then you can bring the voltage up to normal levels.

Line voltage is set to 110 for some extra thermal headroom.

It works, yes!!

The drop is extremely minimal. The output tubes biased right up! I am shocked this works soo well!

 

[Dandy]

Wow, I have one of these scary 83 dudes somewhere. How did you manage the steps you mention above, e.g. preheating and bringing the amp up slowly? Separate switched heater supply and variac?

It certainly makes for an original ST70 pic!

 

[eiraved]

Don't make me rob one off my Hickok to experiment with!

 

[Lavane]

Cool! Now you just need some mercury vapor output tubes.

 

[zackthedog]

I hate to be a "Tube Karen," but it's not going to like that 30uF input cap. They're really designed for choke-input supplies, but if you keep the input cap down to 4uF you can get away with it--maybe. I'd be worried it will arc at some point and damage you power tranny. Just my .02....

 

[Retrovert]

I hate to be a "Tube Karen," but it's not going to like that 30uF input cap. They're really designed for choke-input supplies, but if you keep the input cap down to 4uF you can get away with it--maybe. I'd be worried it will arc at some point and damage you power tranny. Just my .02....

Yeah, totally what he said.

It's a funny example of audio extremism, but I would never, ever run a Hg rectifier on a regular basis even in a transmitter. Better options now exist.

To elaborate on Zack's comment, a choke-input filter widens the conduction angle while a high-value capacitor severely narrows the conduction angle, converting rectification into a square-wave with short duty cycle. All the current is drawn in a very short period of time. The short-cycle for charging greatly stresses the rectifier. It is one thing to use a small rectifier in a tube tester where no current is applied until the "TEST" button is pushed. But in an amplifier? Not so clever.

When, not if, the arc-over event occurs the power transformer go to Valhalla, because if there's one thing a mercury rectifier hates, it is a solo airlift by Valkyries. Many tube rectifiers lost a power transformer in this exact fashion. I suggest adding fuses to ordinary tube amplifiers to protect transformers; this is a case where fusing is mandatory.

PLUS there's a bonus. An Hg rectifier is actually a sort of spark-gap transmitter running at mains frequencies. The only noisier diode is a noise diode, and it carries little current. So the amplifier is now noisy and losing power because of the rectifier's considerable RF hash — readily audible in the AM band using an ordinary AM radio — that is now being spewed and being amplified by the amplifier. Tubes have enormous bandwidth into the tens of MHz, and don't care that the hash is undesirable signal far outside the audio band. This is why such Hg rectifiers in ham gear always used plate chokes. But those had to be carefully placed to avoid creating tank circuits with the power transformer.

The voltage drop across a Hg rectifier also varies with current and temperature.

And if a hot rectifier cracks, it's like breaking a dozen of the older Hg fluorescent tubes.

Using obsolete metal-vapor rectifiers is non-trivial. Don't believe what the Hg rectifier cult says.

 

[zastin17]

Yeah, totally what he said.

It's a funny example of audio extremism, but I would never, ever run a Hg rectifier on a regular basis even in a transmitter. Better options now exist.

To elaborate on Zack's comment, a choke-input filter widens the conduction angle while a high-value capacitor severely narrows the conduction angle, converting rectification into a square-wave with short duty cycle. All the current is drawn in a very short period of time. The short-cycle for charging greatly stresses the rectifier. It is one thing to use a small rectifier in a tube tester where no current is applied until the "TEST" button is pushed. But in an amplifier? Not so clever.

When, not if, the arc-over event occurs the power transformer go to Valhalla, because if there's one thing a mercury rectifier hates, it is a solo airlift by Valkyries. Many tube rectifiers lost a power transformer in this exact fashion. I suggest adding fuses to ordinary tube amplifiers to protect transformers; this is a case where fusing is mandatory.

PLUS there's a bonus. An Hg rectifier is actually a sort of spark-gap transmitter running at mains frequencies. The only noisier diode is a noise diode, and it carries little current. So the amplifier is now noisy and losing power because of the rectifier's considerable RF hash — readily audible in the AM band using an ordinary AM radio — that is now being spewed and being amplified by the amplifier. Tubes have enormous bandwidth into the tens of MHz, and don't care that the hash is undesirable signal far outside the audio band. This is why such Hg rectifiers in ham gear always used plate chokes. But those had to be carefully placed to avoid creating tank circuits with the power transformer.

The voltage drop across a Hg rectifier also varies with current and temperature.

And if a hot rectifier cracks, it's like breaking a dozen of the older Hg fluorescent tubes.

Using obsolete metal-vapor rectifiers is non-trivial. Don't believe what the Hg rectifier cult says.

I never said it was ideal whatsoever. Because i'ts not. It's an incredibly noisy tube. Puts of a ton of random frequencies of all kinds you don't want in audio.

But I'm Sharing because it was a fun experiment.

But I've had it installed for over a week and no problems have arisen. I did because I wanted to see if it worked, and it does. And sounds very dang decent.

I hear nonstop. Things not to do, ect. Because "Boom" and how ideal a component is, or is not.

I do wacky stuff like this all the time, and haven't had a single momentary issue. With a Variac, the risk of arcing seems to be greatly reduced, as I've never lost a rectifier, even the nasty Chinese and Russian ones which should have arced by now.

I also have a underated fuse installed just in case, and through my Panamax which will Cut power the split second their is a fault or short. Or sudden current is drawn.

 

[Retrovert]

I never said it was ideal whatsoever. Because i'ts not. It's an incredibly noisy tube. Puts of a ton of random frequencies of all kinds you don't want in audio. But I'm Sharing because it was a fun experiment.

Uh, you originally wrote:

It works, yes!! The drop is extremely minimal. The output tubes biased right up! I am shocked this works soo well!​

At no time did you mention your awareness that Hg rectifiers emitted broad-spectrum RF hash and that shields are normally used for this reason.

I can only imagine what your neighbor's TV and radio reception looks like. Oh, right, it's all digital streams these days. You kids, you have no idea!

But I've had it installed for over a week and no problems have arisen. I did because I wanted to see if it worked, and it does. And sounds very dang decent.

A week! Wowwwwwwwweeeeee! Well, it's always going to work then! Right, nothing to see, move along then.

In actuality the Hg rectifier does not properly function in this context for the reasons I above set forth and which you grudgingly semi-acknowledge.

The rectifier is spewing AM-band noise into your amplifier and the surrounding environment. Hg rectifiers are normally shielded for this reason. Did you not encounter that in your research? Just because you are not "hearing" that AM-band hash as sound does not mean that the above-described broadband-noise power-suck is not occurring.

I hear nonstop. Things not to do, ect. Because "Boom" and how ideal a component is, or is not.

Uh, yeah, them electrical engineers sure are killjoys! Always sharing their knowledge, experience, and expertise. Constantly "helping" to prevent less-knowledgeable people from blowing up their amplifiers or killing themselves with unsafe practices, "Because 'Boom'". Why, if it weren't for electrical engineers people would be able to have their own laws of physics! Let's throw rocks at them!

Plus all of them audiophile tube losers who make cogent suggestions to keep people from blowing up expensive or unobtanium power transformers. Who do they think they are? Bunch of control freaks, the lot of them! Let's throw rocks at them, too!

I do wacky stuff like this all the time, and haven't had a single momentary issue. With a Variac, the risk of arcing seems to be greatly reduced, as I've never lost a rectifier, even the nasty Chinese and Russian ones which should have arced by now.

As the kids say, I can't even.

With respect to engaging in "wacky stuff" with hot mercury vapor or high voltage, I suggest you look up the phrase "Darwin Award".

My work here clearly is so done no need to put a fork in it.

 

[knockbill]

HA,, this reminds me of the old adage,, ,"its all fun and games til someone puts an eye out!!!"

 

[s-petersen]

I don't care what anyone says, I still think it looks cool....
My shortwave and AM radios hardly work from all of the interference generated by all of the new digital and led stuff.. It seems as though the FCC doesn't care anymore.

 

[analog addict]

Interesting. I've been wanting to design a build with a pair of 816 rectifiers. Yes I know they are an environmental hazard, yes I know they produce X-rays at high PIV, yes I know they generate a bunch of high frequency hash which may require extra measures to control. But I can't help myself, I love they way they look and no, I'm not going to run them in every new build from here on out, I just want one amp that uses these beautiful tubes.

VinylSavor: Tube of the Month : The 816

 

[s-petersen]

Currently I listen a little on my Quad AM3 but there are only some religious channels, a time channel and an old time radio show channel I can listen to when everything else is turned off.
I also have a few Hammarlunds I have been rebuilding

 

[PakProtector]

I have not found noise to be an issue and I ran 816's in a linestage. Currently running 866's in the 6CB5A amps and don't hear it causing an issue. The idea of breaking one hot is giving me pause, and the current build runs 6CJ3 diodes instead. Even those are dropping more voltage than Hg does; that is one of the reasons the testers run 83's, the test voltage is not subject to loading like a hard vacuum diode.
cheers,
Douglas

 

[zastin17]

Uh, you originally wrote:

It works, yes!! The drop is extremely minimal. The output tubes biased right up! I am shocked this works soo well!​

At no time did you mention your awareness that Hg rectifiers emitted broad-spectrum RF hash and that shields are normally used for this reason.

I can only imagine what your neighbor's TV and radio reception looks like. Oh, right, it's all digital streams these days. You kids, you have no idea!



A week! Wowwwwwwwweeeeee! Well, it's always going to work then! Right, nothing to see, move along then.

In actuality the Hg rectifier does not properly function in this context for the reasons I above set forth and which you grudgingly semi-acknowledge.

The rectifier is spewing AM-band noise into your amplifier and the surrounding environment. Hg rectifiers are normally shielded for this reason. Did you not encounter that in your research? Just because you are not "hearing" that AM-band hash as sound does not mean that the above-described broadband-noise power-suck is not occurring.



Uh, yeah, them electrical engineers sure are killjoys! Always sharing their knowledge, experience, and expertise. Constantly "helping" to prevent less-knowledgeable people from blowing up their amplifiers or killing themselves with unsafe practices, "Because 'Boom'". Why, if it weren't for electrical engineers people would be able to have their own laws of physics! Let's throw rocks at them!

Plus all of them audiophile tube losers who make cogent suggestions to keep people from blowing up expensive or unobtanium power transformers. Who do they think they are? Bunch of control freaks, the lot of them! Let's throw rocks at them, too!



As the kids say, I can't even.

With respect to engaging in "wacky stuff" with hot mercury vapor or high voltage, I suggest you look up the phrase "Darwin Award".

My work here clearly is so done no need to put a fork in it.

I dont care. It's my amp, my risk, I can do what I like.

So yes, "put a fork in it"

 

[egellings]

Is the amp noisy with that tube in there? Does the tube cause radio reception interference? I have to admit, it does look cool.

 

[Retrovert]

I dont care. It's my amp, my risk, I can do what I like.

You are being very silly. No one prohibited you from blowing up your own amplifier or spewing RF hash, all to obtain a pretty blue glow.

The key here is the "I dont care." statement in response to a clear explanation of the issues including why Hg rectifiers must be shielded and why use is generally deprecated.

 

[Dandy]

Some useful practical information and warnings here: http://www.uli.de/tubes/83.htm.

"Generation of high-frequent (RF) noise by the arc igniting at each half-wave (what it does very rapidly, thus generating high spikes) is prohibited by inserting a small toroidal choke (1 mH or more) in series with each anode lead. Gas rectifiers are a perfect choice for tube-HiFi-amplifiers, but changing over from high-vacuum or semiconductor rectifiers requires a very skilled technician - some startup and preheating circuitry must be added and - most probably - especially be developed first."

 

[PakProtector]

Yeah, pre-heat is needed...Amperite did a fine job there. Delays on their 'NO' series available in like 15 second intervals. 30 sec to heat up for a pair that sees regular use is just fine. I have all the heaters on one trans, and the plate iron fired with the Amperite relay. Don't follow the insane, if it sits you have to warm them for days advice...if you let 'em cook too long you poison the cathode and it is game over. 5 mins should do fine... The 866AX are smaller( skinnier ) and have little more than is needed in terms of Hg dosing. The RCA coke bottles with large shield to anode spacing look WAAAAAY cooler though...

Douglas

 

[arts]

I have a bunch of SWL cards from across the world from the days when you could send a listener report to the station with the SINPO and a postal money thingy (can't remember the term, reply coupon maybe). Days gone for good.

Wasn't that a QSL card?

 

[Retrovert]

Amperite did a fine job there. Delays on their 'NO' series available in like 15 second intervals. 30 sec to heat up for a pair that sees regular use is just fine. I have all the heaters on one trans, and the plate iron fired with the Amperite relay.

The Amperite is totally old school. The Tek 500 series had a few of them. I remember my 585 had them. Plus an HP scope of that era. And RF amplifiers used them.

The Amperite, however, has limited current capability, and must drive an external relay. It also does not protect against hot switching because, being hot, it remains closed. (Not that anyone ever does that, or experiences mains dropouts, which never occurs.)

I was once asked to fabricate a power-on delay using Amperites to control delayed heaters, B+, and screens, separate delays for the preamp and power amp stages to prevent thumping. My response was, well, the 555 was a better solution and less expensive. No, the answer came back, I don't want sand in my amplifier. Then he found out how much the Amperite tubes would cost, plus assembly, and the interest evaporated.

I have used a 555 to drive a small power-on relay, with the delay being set using dip switches for different resistors. Beyond variable delay, the substantial advantage is that the 555 resets itself after a power cycle and begins the cycle anew, so no risk of hot cycling. (Again, never happens.) Lower cost and easier to use than the Aperite, which was perfect technology for the 1950s and 1960s. But it was game over for the delay tubes circa 1971, when the 555 was introduced.