I just substituted a 5V4G for the original 5U4G that was orinally designed for a Sun Audio amp. At the first initial turn on, there was momentary flashing. But it only happened ONCE when I used the 5V4G for the first time. It did not exhibit any flashing since then... What could've caused the flash? I also replaced a JAN Philips 6X4 with a Mullard in a preamp. The Mullard has strong initial flashing like a flashlight bulb, but unlike the 5V4G, it always does flash at every turn on....
I a bit confused here... as you can tell. When you said that the 5V4 rectifier "flashed" once---but, never again, you meant that the 5V4 is still working, right? Or did it flash and die?
The 5V4 and the 5U4 have pretty close to the same PIV = 1500 volts. The big difference is the MAX current output per plate 275mA DC for the 5U4 and 175mA DC for the 5V4. Peak current per plate = 525 mA (5V4-GA) and 1000mA (5U4-GB).
Now, I know this sounds silly, but I've seen 5Y3GT in 5AR4 OEM circuits. And the amp sometimes runs into problems when it is really pushed and the power tubes demand so much current, that the current draw actually arc-welds the 5Y3GT. The power tranformers on these amps are usually the big over-engineered type.
But, I've yet to see a 5Y3GT (400 mA max peak per plate) fail, when it is replaced into a 5AR4 socket (750 mA) and the amp is simply turned on, under no load.
I use 5Y3GT in most 5AR4/GZ34 amps which I rebuild, to "form" new capacitors. This is because the 5Y3GT is directly heated and therefore the tubes "see" voltage from the first application of AC voltage from the Variac.
I don't keep the 5Y3GT in these amps, but I've yet to have an arcing problem, using them to form new caps, up to max 120 volts AC---where there is no input (volume at zero), speaker attached, power tubes at idle.
I know a lot of folk wince, but some guitarists will put the 5Y3GT into an amp which normally takes a 5AR4/GZ34 recitifer, to give the amp more "sag." Especially, those amps with undersized power transformers. DEFINITELY, not recommended. But, these amps actually work at volume.
Now, since you said that the Mullard 6X4 "flashes" all the time---I have a feeling you are talking about the initial glowing of the heater filament. Since the 5U4-GB has no separate heater filament, you see no flash. But, when you replaced it with that 5V4-G, you noticed the heater filament initial glow.
Sorry if I wasn't clear. The 5V4G is still working (although more brightly lit up compared to the stock Sovtek 5U4G), the flash only happened the first time I installed it. I actually saw a tiny bit of spark too (arcing). After that it seems to work fine at every turn on, there were no flashes anymore. I still have a large base Mullard 5AR4 that I tried in an Anthem preamp I sold years ago. I tried it in the amp, it gives a robust fast-full bass, with dark lower mids, but it laso gives a bit of fatigueing edge to the tone compared to the RCA 5V4G. BTW the stock OEM Sino 5U4G for the amp sounds brittle compared to both the Mullard 5AR4/GZ34 and the RCA 5V4G I recently acquired. I guess I really should just stick to the original designated rectifier (5U4G) to be on the safe side. Is the 5AR4/GZ34 an "okay" sub for the Sovtek 5U4G for the meanwhile until I get a good better 5U4G/GZ32? I forgot to mention that the Sun Audio stereo amp has a choke in the PS section.
The JAN Philips ECG is atcually 6X4WA that was replaced by a Mullard 6X4. The Philips never exhibited any flashing when it was the one in constant use, that's why I was wondering why the Mullard 6X4 does this all the time at every turn on. It sounds much open and airy than the Philips though. The only thing I considered is that every tube maker has a different internal structure eventhough they are direct replacements or the same types, so maybe that's why they have their own idiosyncracies (flashes at turn on)... BTW, the stock 6SN7GT drivers are now also replaced by 5692's, I know it also has diff. parameters, but they sound better than the stock Russians they replaced. There's also the Mullard ECC34 I kight try some day, it has slighty lower gain than a typical 6SN7, but reportedly sounds very good.
Derick, as Steve rightly points out, the 5V4 is NO sub for a 5U4G, and in a Sun amp, it pumps way too much current for a 5V4 to handle. The 5V4 is rated MUCH less than a 5U4. When you see arcing on startup, you are causing damage to the amp. Continued use of a 5V4 in this amp will cause power supply cap failure, and when they arc for the last time before blowing out, they may very well take the power tubes with them.
You should never do this kind of thing, subbing a wrong tube in is almost always a disaster waiting to happen.
In the Sun amps, you can sub a 5AR4 (only a NOS one) for the 5U4G, this will reduce the headroom a little and raise the operating point of the power tubes. It is also ok to sub a 5R4, this will drop the operating point a bit and give a slightly more open sound.
Thanx for advice Robert, I was naive and stupid about the current draw, and ignored it as they both are rated at 5V. I'll just use the Russian 5U4G for the meanwhile instead I guess. The large base Mullard GZ34 seems to lack headroom when I want more volume alright. And thanx for the reassurance that the Mullard 6X4's flashing is normal. I hope the amp is fine though *fingers crossed*.
Yeah, the voltage drop on the GZ34 is much less than a 5U4G, so that'll drop the headroom a bit much.
You can get some very good 5U4's for a reasonable price that will give you a big time better sound, look for Tungsol 5U4GB's - which are knock-out fantastic, also don't discount 1950's/early 60's GE 5U4GB's which are very good too, both can be found for a reasonable price.
I've seen GE 5U4GB's which have a straight glass compared to the coke bottle type typical of 5U4G's. Are these the 50's-60's types you recommend? Maybe there are Bendix type 5U4's too....
No, there never was a Bendix 5U4 type made. Bendix tubes can be variable in sound anyways, some are good, others not so.
There are GE 5U4GB's of every vintage imaginable. GB's are always straight glass. Don't get hung up on the fetish of believing the older coke bottle types are always superior, some are great - old Tungsol, Sylvania, for example, some are not so spectacular - the NU, KenRad come to mind. Some GB's are awful - later Sylvanias are one - but late 50's Tungsol, RCA or GE are very good.
There never was a good Euro 5U4 type, except the GEC U52 which is very good, and Mullard GZ series. There are some god-awful Euro types floating around with names like Ultron, etc. which are to be avoided.
5V4s do not have (to my knowledge at least) any form of "instant- on" filament; this would be redundant as an indirectly heated rectifier solves the cathode stripping issue for output and front-end tubes. While an "instant on" might help the lifespan of the rectifier, the materials used for this special filament type will not bear the temperatures and electrical loads generated in a 2-3 ampere heater-- hence its' use in small signal tubes exclusively. (If power tubes could be made with it, the delayed ramp up of the DC w/ indirect rectifiers would be unecessary.) The flash you saw was an internal arc caused by the excessive voltage and current demands meant for a 5u4; it only did it once because (sorry) you damaged the emission capabilities of the tube. When subbing rectifiers, look in a tube manual for 3 critical ratings: 1. Filament Current-- a GZ34 is 1.9 amps and there are common rectifiers that draw 3+ amps 2. PIV (Peak Inverse Voltage) This figure is double the operational B+/DC of the amp. 3. Maximum capacitative load. The 5V4 and 5R4 are the lowest, at 10 and 20 (I think) respectively. If you wish to add more storage, add a small choke (1-3 henries, 200 ma or so-- Ned at Triode Electronics has them) and connect one choke lead to the small 1st cap (10 uf for a 5V4) and the other choke lead to a 100 uf or so electrolytic bypassed with a 10-20 uf Solen FastCap. If the bypass uf value is any less than 3-5% of the larger caps' uf value the benefits will manifest only in the extreme high frequencies. I have a computer modeling program that shows curves of various chokes and capacitors with and w/o bypasses; for example, a .1uf bypass on a 100 uf 'lytic will have no effect below 15,000 hertz. Chris
Compared to 5U4, the 5V4 is a light-weight tube and should not be used in place of 5U4. One reason is it will only drive 10uF of capacitance on the cathode. More capacitance than this and it will arc, maybe only occasionally but will finally fail. Check the data sheets.
The 5V4G is an indirect heated-cathode rectifier and the 5U4G is a directly heated cathode tube. Maybe the "flash" you see with the 5V4G is the heater element warming up.
When you said that you replaced the Philips 6X4 with a Mullard, you mean a Mullard 6X4/EZ 90? The 6X4 type is indirectly heated. So. once again, you may be seeing the heater filament light up, initially on fire-up.
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