Rectifier Tube

[primosounds]

I still like the Chinese One Electron brand 5AR4s. Have one in a Scott LK48 for about 100 hours now, without any problems. The Sovteks' are good too. Or spend big money on Mullard 4 notch or 9 notch rectifiers. The communist countries are probably the most experienced at making vacuum tubes because they never stopped, like western countries did 30 years ago.

tick, tock, tick, tock..... time is running down
Making the tube is not the issue. Have you ever seen the video of the guy making a vacuum tube from scratch? To make it reliable and with longevity requires special metallurgy of ultra pure metals as well as special coatings and gases which are of a proprietary nature.
The other thing to consider is that when the rectifier fails it may take out other components. Replacing a transformer is more expensive than a Mullard 5ar4 or doing the SS back up procedure.

 

[Palustris]

The rectifier line [sic] on the OEM PA-060 power transformer is rated at 4 amps

With a 4 A filament, the 3.75A 5AU4, a more robust 5U4GB with low insertion loss, at $15 on epay is the obvious choice. Few will use it, except for the veteran DIYers, because despite its better specifications and better sound, it is not as well known as the Mullard GZ37.

All that said, and in response to the original question, the B+ current requirements for the Dynaco Mk IV are well within the capabilities of the current production 5AR4. It is only the ST70 and its modern variants that require more B+ current than the current production 5AR4s are capable of reliably providing.

 

[gadget73]

honestly an ST-70 wants more current than a vintage 5AR4 is officially rated to provide too, though those do seem to suffer the abuse better. Modern 5AR4's really do seem to live by their datasheet specs and do not handle additional demands overly well.

 

[canton]

OK so it looks like for some new Rec tubes it is Mullard $40===Groove $32===Geneflex$40 for the 5AR4's any thoughts? Also Ruby Tubes for $25 at the guitar shop have been brought up.


I will do a separate post on the very old tubes I own that are what 5Y4's or 5U4G coke bottle style tubes see what the use and thoughts are on those.

Canton

 

[paysonmark]

Great thread, lots of good info. Im needing to get a new rectifier tube for my ST70 , AES in AZ tested mine and called it weak!
What is the diode protection mod people are referring too. thanks all

 

[paysonmark]

With a 4 A filament, the 3.75A 5AU4, a more robust 5U4GB with low insertion loss, at $15 on epay is the obvious choice. Few will use it, except for the veteran DIYers, because despite its better specifications and better sound, it is not as well known as the Mullard GZ37.

View attachment 1191313

cool
I can get these locally, just to be sure, they will work in my stock st70 with out any issue

 

[triode17]

tick, tock, tick, tock..... time is running down
Making the tube is not the issue. Have you ever seen the video of the guy making a vacuum tube from scratch? To make it reliable and with longevity requires special metallurgy of ultra pure metals as well as special coatings and gases which are of a proprietary nature.
The other thing to consider is that when the rectifier fails it may take out other components. Replacing a transformer is more expensive than a Mullard 5ar4 or doing the SS back up procedure.

I figured someone would argue this. If you are referring to the French engineer who makes a miniature tube, that's fine but it's a mini, which should last 5-10 thousand hours. I did add a fuse on the high voltage secondary though, as a general precaution.
Side note: The SS diodes in series with the rect. tube is good but how would you know if the tube failed? Suddenly, your B+ goes up 30 or 40 volts and in the case of an ST-70, the screen grid voltage is now way above it's rated maximum. That's another reason I like to use KT77s that are rated 800v plate, 800v screen.

 

[Retrovert]

Side note: The SS diodes in series with the rect. tube is good but how would you know if the tube failed? Suddenly, your B+ goes up 30 or 40 volts and in the case of an ST-70, the screen grid voltage is now way above it's rated maximum. That's another reason I like to use KT77s that are rated 800v plate, 800v screen.

Sigh. No, that analysis is 100% incorrect.

You know the rectifier has failed because the B+ STOPS. The solid-state diodes are wired in series with the tube rectifier's pins. The purpose is to take up the slack in reverse voltage, as this stresses a tube rectifier but not the solid-state rectifier. The 0.7 VDC voltage drop from solid-state, by the way, is negligible for B+ so it can be ignored.

All current flows through the tube, cathode to plate. All of the current. Every single electron.

So, no, the voltage does not suddenly rise if the rectifier fails, and there is no safety drawback. The advantage is extension of the tube rectifier's lifespan, always a good thing as rectifier tubes cost real money.

 

[Palustris]

Triode Electronics Dynaco PA060 replacement power transformer:

Secondary B+ winding is 720VCT (360-0-360) at 300 ma with 55V bias tap, plus two 6.3VCT 5 amps & one 5V 4 amp tube filament & rectifier windings, and 55V bias tap.. Can use solid state rectifiers or any single tube rectifier with filament up to 5V at 4 amps (or 2 5AR4/GZ34 could be used in parallel) & sufficient B+ current rating....usually, 5AR4 or 5U4. (note, watch that the voltage isn't above capacitor ratings if solid-state rectifier is used!)

 

[whoaru99]

Triode Electronics Dynaco PA060 replacement power transformer:

...

FWIW, that is an "upgrade" transformer not OEM in the sense of Dynaco. OEM, I suppose, if one built the Triode variant of the amp.

 

[paysonmark]

Do not assume that PT can handle a @4A filament until you see some Dynaco sourced specs. It's limited by the ST-70 manual to using a 5U4 for limited troubleshooting @3A.

I'm trying not to assume, I'm a tube nubee,
and that's why I'm asking from the people here who know

 

[airtime]

I've been using two new Genelex Gold Lion rectifier tubes. They held up better then my Sovtek which failed after about two years.

Contact Jim McShane for the best fit for your amp and needs.

 

[sKiZo]

If you can show where you dug this up, it would be news for everyone. I've looked for a Dynaco published spec rating on the 060 and haven't found anything that gives the official rating for that winding.

oOOps - I gotta stop making late night posts. Correct that to 3 amps. It's the newer iron (VTA, Dynakit, and the like) that are rated at 5 amps. Original post corrected.

 

[Lavane]

So, if you have the VTA, Triode or Dynakit ST-70 power trany the 5V3A rectifier sounds like the better choice. Is the 5V3A a faster start rect I fire like a 5U4?

 

[whoaru99]

So, if you have the VTA, Triode or Dynakit ST-70 power trany the 5V3A rectifier sounds like the better choice. Is the 5V3A a faster start rect I fire like a 5U4?

I suggest caution replacing an indirect heated rectifier with a directly heated one.

The direct heated starts passing current very quickly, before indirect heated tubes start to conduct. This can cause the B+ to surge high before the load of the other tubes pulls it down to nominal working level.

If there is plenty of cushion in the capacitor voltages and other parts voltage rating it may not be a big deal in that regard. But, if there isn't much cushion the initial voltage surge could cause problems.

 

[Lavane]

I suggest caution replacing an indirect heated rectifier with a directly heated one.

The direct heated starts passing current very quickly, before indirect heated tubes start to conduct. This can cause the B+ to surge high before the load of the other tubes pulls it down to nominal working level.

If there is plenty of cushion in the capacitor voltages and other parts voltage rating it may not be a big deal in that regard. But, if there isn't much cushion the initial voltage surge could cause problems.

Thanks! That's the kind of info I needed.

 

[sKiZo]

I suggest caution replacing an indirect heated rectifier with a directly heated one.

The direct heated starts passing current very quickly, before indirect heated tubes start to conduct. This can cause the B+ to surge high before the load of the other tubes pulls it down to nominal working level.

That's where a thermistor on the main AC power can come in handy - those ramp up slow enough to compensate. Trade off is they never open completely, so you can expect some loss, and they run HOT under load, so you need a lot of air clearance around them.

A real killer is quick power blips like you might get in a thunder storm or relay issue on the grid. Tube equipment needs a bit of time to discharge properly before hitting them with another on rush surge. I've been using an adapter (TRC 90033 Shockshield) on the power line that requires a manual reset any time the power goes out to avoid that.

 

[whoaru99]

Not sure if all of those are equivalent but if the primary is upgraded to 120v then you'll get the benefit of a more accurate B+ on your line voltage and if you then use the 5V3 with its 40 -50v of drop, as opposed to the 5AR4's, I can't see how there would be any concerns about the directly heated cath. and B+ voltage pushing cap limits.

Voltage drop is contingent on load. Until the remaining tubes begin to conduct there is essentially no load. Meaning, B+ surges until then.

 

[primosounds]

So, if you have the VTA, Triode or Dynakit ST-70 power trany the 5V3A rectifier sounds like the better choice. Is the 5V3A a faster start rect I fire like a 5U4?

Like 99 said if you use the directly heated rectifier like 5u4 or 5v3 there will be a large voltage increase before the rectifier and other tubes start to draw current and pull the voltage down. The 5v3 passes more current than the 5u4 but otherwise very similar. You need to be sure your capacitors are rated for the voltage surge so they don't blow up or break down.
The original Dynaco manual recommends using a 5u4gb if high wall voltages are a problem. So, it seems that the 5v tap is rated for 3 amps.

 

[airtime]

So, if you have the VTA, Triode or Dynakit ST-70 power trany the 5V3A rectifier sounds like the better choice. Is the 5V3A a faster start rect I fire like a 5U4?

I'm using the VTA ST-70 with KT-88's and I'm using the Genelex 5AR4 with NO problems.