yes on that sparking/dead JJ 5AR4. One of the reasons I'm curious about this tube, Visual inspection of the cathode shows those hot spots, but as you say, once the cathode is warm, it operates normally. Sparking seems to be increasing at each successive power-up, let's see how long it lasts.
anecdotally, I've been using a RCA 5U4GB in this amp for 2 years, no issues. $20 on ebay. But I love the hanging filaments on this tube, and the big shouldered bottle.
anecdotally, I've been using a RCA 5U4GB in this amp for 2 years, no issues. $20 on ebay. But I love the hanging filaments on this tube, and the big shouldered bottle.
Hi George,
Well, you are running them hard by your own admission. Most equipment designed "back then" was conservatively designed. Normally I don't have a problem. You are quite right too, they carry all the DC current needed by everything. But they generally operate fine as they are designed for that service. They often outlast the output tubes.
Filament rectifiers can "sparkle" sometimes. But a 5AR4 doesn't heat up quickly so it conducts more gradually. Only cheap tubes and poorly designed circuits seem to kill them. That's in my experience anyway.
Hi wg_ski,
Agree completely, including your design direction.
Well, you are running them hard by your own admission. Most equipment designed "back then" was conservatively designed. Normally I don't have a problem. You are quite right too, they carry all the DC current needed by everything. But they generally operate fine as they are designed for that service. They often outlast the output tubes.
Filament rectifiers can "sparkle" sometimes. But a 5AR4 doesn't heat up quickly so it conducts more gradually. Only cheap tubes and poorly designed circuits seem to kill them. That's in my experience anyway.
Hi wg_ski,
Agree completely, including your design direction.
Do you have a lot of filter capacitance on the tube? That would cause tube antics on startup but settle out after the caps have reached operating voltage. Peak charging currents would shorten tube life.Greetings, friends. I put a new-to-me rectifier tube in my amp, and it does this:
Tube is a Soviet 5Ц3C, which I believe to be their version of the venerable 5U4G. Amp is fairly low voltage, tube sees maybe 350v on each anode and makes around 130mA. It does this crazy dance at startup (5 times so far) and then behaves normally.
So what gives?
Yes, sorry for not posting schematic earlier. 32uF reservoir cap, 10H choke, 32uF, then 1H choke, then 100uF cap before OT. Still unsure how to determine series resistance, so maybe that's a problem.
Started out life as a Lacewood 2.0 from CascadeAudio.com but I've modified it to run 6B4G tubes.
Single-Ended DHT Amp Schematic - 6B4G + 6SL7
Schematic needs updating, driver tube is now operating with 100K + 2K2 resistors.
Single-Ended DHT Amp Schematic - 6B4G + 6SL7
Schematic needs updating, driver tube is now operating with 100K + 2K2 resistors.
Thanks. I kinda figured this was a single ended amp. Not surprised the Russian 5U4G variant is arching with C1 @32uF.
jeff
jeff
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I've been specifically advised, by Matt of CascadeAudio, that the Hammond 193J is not a "Swinging Choke" and is not appropriate for a choke-loaded supply.
But I guess that's technically hearsay. And I've seen amps that use lower-rated chokes in their supplies, so I dunno.
But I guess that's technically hearsay. And I've seen amps that use lower-rated chokes in their supplies, so I dunno.
And the transformer has the minimum resistance required without needing additional as described in 5U4G datasheet ?
Soviet 5Ц3C is probably worse in that aspect
Soviet 5Ц3C is probably worse in that aspect
Ya. "Series Resistance" still a bit of a mystery to me. Is it the resistance in the trafo, or in the filter side of the supply?
If there is an input cap it is the resistance in series with the tube up to the cap , that is like a short circuit at startup
For a transformer Rtotal = Rsecondary + n^2 x Rprimary
n is the turn ratio of the transformer to half secondary , and Rsecondary is from central tap to each plate of the rectifier
Looking at the specs I doubt that Hammond has enough resistance by itself ... soviet 5Ц3C is much worse , the max input cap stated is just 20uF
For a transformer Rtotal = Rsecondary + n^2 x Rprimary
n is the turn ratio of the transformer to half secondary , and Rsecondary is from central tap to each plate of the rectifier
Looking at the specs I doubt that Hammond has enough resistance by itself ... soviet 5Ц3C is much worse , the max input cap stated is just 20uF
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The equivalent series resistance is a factor for continuous operation and steady state peak plate current (800mA for 5U4G). Your problem is the startup transient peak plate current (4A for 5U4G). The power supply design shouldn't be having a problem with a spec 5U4. My guess is that the Russian tube you have in there is below spec. The Hammond transformer should have sufficient series resistance. You said it sees about 350v per plate. The necessary effective series resistance needed is only about 50Ω. The Hammond should naturally exceed this.
You should try calculating the effective series resistance of the transformer primary. Read here: http://diyaudioprojects.com/Technical/Tube-Power-Supplies/Basic-Tube-Power-Supplies.pdf or go directly to the Reich reference.
You should try calculating the effective series resistance of the transformer primary. Read here: http://diyaudioprojects.com/Technical/Tube-Power-Supplies/Basic-Tube-Power-Supplies.pdf or go directly to the Reich reference.
No, that Hammond choke will not like choke input. But you can use a small cap in front of it, like .47uF. But really, just reduce that 32uF to 4 or even 8uF.
There's no reason to change anything. The OP's amp works fine with real 5U4's. Obviously, the Russian tubes (@4uF input C) aren't actually the same spec as a 5U4G/GB.
jeff
jeff
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I may have missed it, but what tis the AC voltage of the HV secondary winding on that 5U4?Yes, sorry for not posting schematic earlier. 32uF reservoir cap, 10H choke, 32uF, then 1H choke, then 100uF cap before OT. Still unsure how to determine series resistance, so maybe that's a problem.
The effective winding series resistance does certainly play a part in determining the initial transient peak plate current.The equivalent series resistance is a factor for continuous operation and steady state peak plate current (800mA for 5U4G). Your problem is the startup transient peak plate current (4A for 5U4G).
The schematic of the power supply in post #24 doesn't show series ss diodes with the valve anodes.
Doesn't show the heater wiring, either. Things are assumed.The schematic of the power supply in post #24 doesn't show series ss diodes with the valve anodes.
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