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For a 650v HT supply with a hybrid bridge, what are the choices for tube rectifiers?
Particularly interested in damper diode choices since I have a stock of 6DT4 and 6AU4
Andy
Follow Ups:
Hi Andy,
you have not specified the current you need to draw.
Although I generally prefer an all tube bridge, I don't mind a hybrid bridge either if space is restricted.
6AU4 will surely do nicely (depends on the current you need). In case of a hybrid bridge, I would connect the heaters of the dampers to B+ to ease stress on the heater-cathode insulation.
The hybrid bridge with 6AU4s or other dampers will have a nice slow start up and retain pretthy much all of the tube rectifier characteristics.
If you want some cooler looking rectifiers, you could use a pair of 836. They have indirectly heated cathodes but theye are connected to the filament in the tubes themselves. 1616s would be a DH alternative. But these transmitting type rectifiers have high filament current demands.
Best regards
Thomas
Hi Thomas,
Thinking about a SE amp using a transmitting triode instead of the usual 300b. Choices - 211 and 845 are expensive, 813 is big and greedy, so looking for some cute options a bit off the beaten track.
Looks like the 814 is interesting and good value. There's also the 828 but that's rare and pricey - virtually the same but just a bit more poke. Radio hams still have some 814s in odd boxes. It's never been popular. Is there something I should know about using this tube? Looks good in triode.
So current would be about 60mA for each 814. Add 20mA for a driver and 5mA for an input tube and total would come in at under 200mA for a stereo amp. I don't see it needs over 650v HT for a typical domestic room with fairly sensitive speakers.
Once an amp was built it would be possible to play around with other transmitting tubes. I use a modular chassis anyway, so can swap output top plates without disturbing the rest of the amp.
Andy
Hi Andy,
A pair of 6AU4 can easily supply that kind of current. If you go for this kind of transmitting tubes with top caps, The 1616 or 836 would be a nice match aesthetically. 1616 is often cheap, 836 a bit more pricey
Thomas
Andy,
The 6AU4GTA is a great tube, but you need a pair and "gobs" of heater current. A 5AR4/GZ34 doesn't exhibit much more forward drop than damper diodes, uses a single socket, and "only" 2 A. of heater current. A reasonably priced Sovtek 5AR4 on the "hot" side of the bridge will be FINE combined with 2X 1200 PIV/2 A. Cree C4D02120A 2nd generation SiC Schottky diodes on the "cold" side. The is no arc over worry and zero switching noise to sneak into the power trafo.
The prices of the 2nd generation 1200 PIV SiC parts are reasonable.
Eli D.
I wasn't aware that GZ34 was comfortable at 650v? In particular the Russian ones have blown up in the past in amps I built.
But what about the voltage for these damper diodes - 6AU4 etc? It doesn't specifically say anything in the data sheets for continuous use. Anybody know?
Andy
"I wasn't aware that GZ34 was comfortable at 650v? In particular the Russian ones have blown up in the past in amps I built."
The 5AR4/GZ34 isn't "comfortable" at 650 V. of B+, IF the setup is FWCT. However, the PIV rating is not close to being exceeded in a bridge setup. ;> )
Yes, Russian 5AR4s tend to misbehave at the top of the documented voltage range, but you are building a bridge and the SS diodes alone can "hold the fort down". Remember, in your bridge, a high PIV SS diode is in series with a vacuum diode at all times.
Eli D.
Andy,
Go with damper diodes.
Reportedly lower switching noise that the usual candidates (search Lynn Olson via google - suspect that you've already done so)
Hey, I've been using 6D22S for years.. and guess what; they still work. Ratings are well within your means and I believe that PY500A as mentioned by another is quite similar.
Dont get roped into the U52 v xyz game, save your bucks.
Regards,
Shane
PY500A
The hybrid bridge is excellent no matter what others may say. The hybrid bridge produces 1/2 the PIV. I prefer 6AX4GT with 900 volts cathode to filament insulation. Performing simulations on PSUD2, the 6AU4GT produced more low level noise for unknown reasons.
Another idea is 5R4GY - common enough. The issue here is voltage drop and the 4uF capacitor.
If you used two of them, how would this improve voltage drop? Is there a formula?
Could you increase the input capacitor size at all, and if so to roughly what?
Andy
It's always valuable to read the data sheets carefully. In the Tung-Sol sheet for this tube, no maximum capacitor is specified, just the maximum peak current per diode. PSUD will tell you this number, it is a combination of the capacitance, the impedance of the transformer, the voltage, and the current draw.
What IS specified is a few "typical" conditions, including the resistance of the power transformer.
For those of us with Macs, what do we do about PSUD?Andy
Edits: 06/29/12
Run a Parallels or Bootcamp with a minimal Windoze installation for PSUD only, Parallels is neat and you can start up and run Windoze concurrently, then shut it down when you're done without needing to reboot your computer.
If you use a Windows simulator, do you need to get into all the firewall/anti-virus software you need for a PC? The MAC is mercifully free of most of these issues.
Andy
Absolutely not thank Chris Tafari !!
The key thing is to remember to turn off your wi-fi or pull your Ethernet plug when you fire up the Dozer.
I use it exclusively to run a few applications which are unfortunately not yet available to OS X, and make a point of ensuring that there is no access out of the box when active to keep the machine bug free.
You could, if you're totally paranoid, download PSUD etc.... to a USB stick using another pc, and scan the stick for bugs PRIOR to copying the contents over to your Mac.
For this range of voltage, you've rule-out solid-state rectification? Would seem a bit more reliable. JMO.
Solid state is a choice, indeed. But a hybrid bridge is not too bad, and tubes sound nice. I guess I'm just a bit traditional!
What would you use for solid state at this voltage?
Andy
I'd use a simple UF4007 bridge or UF5408 for more stiff PS. NP bypass caps to reduce hash. Usual setup, nothing fancy.
.
Nice slow beginning for B+ and heaters, and even slower for B+.
Reliable and low-cost.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
I've had better luck & reliability using solid-state rectification. Bypassing for hash and using slow-warmup devices, like Timbo posted. Not that there aren't tube rectifiers in the voltage range you are using. But, kinda getting a bit hard to find. And $$$. And still maintain long-term reliability.
You can always put a socket onto the chassis and bypass the tube rectifier (adding one later, if you find a good NOS---removing the SS portion--- or add SS inline to help alleviate some transient issues.
I know, I know--- sacrilegious, for a tube board. Just my current (sorry for the pun) experience with guitar amps.
Hi!
I've used TV damper tubes for rectification of such voltage levels and even much higher up to double this kind of voltage.
No reliability issues whatsover.
And they are dirt cheap!
Thomas
I can't tell you how two would factor but I've been running an amp with a 47uf input cap, using RCA, RTC and Raytheon 5R4's for a couple of years with zero issues and no arcing in any of the rectifiers at turn on..... although I recently acquired a case of Nos GEC U52's (labelled 5R4GY) which drop much less voltage and sound vastly better !
The 4uf spec on the 5R4GY seems way too conservative. In my main preamps, I use a 5R4GY feeding a 50uf or a 100uf cap, and I have had no reliability problems after 5 years. Both preamps draw a fairly hefty current at a moderate B+ (about 70ma at 240v in the preamp with 50uf, and 20ma at 400v in the one with 100uf). I don't know how this would translate to a power amp drawing, for example, over 100ma at 500+ volts, but in general it seems quite safe to operate the 5R4GY into a bigger cap than 4uf.
I think the 4mfd cap suggestion is based on the condition when max fully loaded plate to plate AC supply voltage are applied. For "civilian" use, I don't think the tube will break a sweat even when we go over 4mfd. However, what is the limit, I have no idea.
On my preamp, my first cap is 20uf, B+ is 280vdc, my CV717 British version of 5r4 still tested like new after 5 yrs.
Hmmm - 47uf with a 5R4. that's interesting. I have a few 5R4GY.
Did you try those yet with your 47uF input cap?
Andy
I find DHT rectifiers sound better with a small input cap . The P.I.T.A thing I find about 5R4 is the volt-drop . Use in parallel for best reults with these things...
Also i forgot to ask : what HT transformer are you intending on using ? Remember I have 11H/65R/200mA(potted) and 9.5H/45R(bell-ends) chokes if you need any
Al
Yep have tried them all, also 5R4WGB & 5R4GYS... no problems whatsoever.
Interestingly there is one variant I tried which does very marginally arc over at switch on, only when my ac mains voltage is elevated more than ~10% above nominal (it does fluctuate quite randomly and is typical of most mains utility supplies anywhere I've lived !).
This 5R4 variant is the one which is apparently claimed to be the most rugged of all however, the potato masher styled BENDIX super beefy military red labelled 5R4WGB with the VERY thick glass and 4 thick metal rod supports internally.
The less weighty potato masher Raytheon 5R4WGB has absolutely no issues with the 47uF input (600V Mundorf TubeCap) in this amp.
You might however also consider the 5U4GB which can readily cope with significantly larger input caps again and is specced for a nominal 40uf.
If heater current is an issue then the GEC U52, GEC's version of 5U4 only draws 2.25A of filamanet current instead of 3A rating of typical 5U4's
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