Questions about subbing a 5R4 Rectifier in my Accomplice in place of the 5AR4

[Platefire]

In my Allen Accomplice I've been running JJ 6L6GC's Biased at 396.6V/44.8 mA and 396.5V/46.2 mA

My Sovtek 5AR4 just died. I went through my tube stock and had a 5U4, 5Y3 and 5R4. I chose the 5R4 knowing that it produces lower voltage and only requires 2 amps heater current. I can tell it has less clean headroom. All and all still sounds pretty decent. Not sure what the plate voltage currently is but the bias is now running about 30mA on each power tube.

Just wondering would it be safe to run it for a while like this until my new 5AR4 comes in????? or would it be better to let her rest until my replacement rec comes in. Thanks, Platefire

[CO_Hoya]

I'm just a noob, but my understanding is that the 5R4 is directly heated, similar to the 5U4, and so has a fast turn-on.
The 5AR4 is indirectly heated and so slow turn on.

Whether the Allen Accomplice can deal with a fast turn-on is not something I can answer.

Here's one of the myriad tube rectifier comparison charts on-line that delineates the heater type (from here):

[sluckey]

Just wondering would it be safe to run it for a while like this until my new 5AR4 comes in?????

That's fine. I've been running a 5R4 (potato masher) in my Sunn for 16 years.

[ac427v]

I use them to intentionally drop voltage in an amp. Works great for that. But I don't know how to calculate the safe size for the first reservoir capacitor. In ignorance I have limited it to 32uf so I don't learn the limits from bad experience.

[Platefire]

Ok, thanks. Good! I got 3 large G.E. 5R4's. Regarding quick warm up, I always leave my standby on about a minute prior to turning on the big DCV. Don't know if it really helps, but makes me feel better. Platefire

[Platefire]

Got a dumb question I reckon. My intentions was to run this 5R4 rectifier in place of my downed 5AR4 until the replacement arrives in shipping. sluckey said he's been running a 5R4 for years in his Sun---but didn't mention bias? To be honest I'm kind of liking the sound of the change with the voltage drop and I haven't touched the bias. So I was wanting to experiment a little with the voltage drop and existing bias setting. So I just wanted to be sure that was safe!!!

When I first installed the matched pair of JJ 6L6GC's with Sovtek 5AR4 rectifier, the loaded voltage was running 397VDC. So the rectifier chart posted by CO-hoya shows the 5AR4 at 402VDC minus 5R4 367VDC=35VDC Voltage Drop So my last checked plate voltage at 397VDC minus 35VDC drop=362VDC Estimated dropped Plate voltage. My bias is currently reading 30 mA on each tube. I realize this is just a loose guesstamate So-----I'm thinking this is a cold bias and so my power tubes would be perfectly safe as is? Is that right??? Just making sure Platefire

[sluckey]

I bought my Sunn on eBay with no tubes. Schematic calls for 5AR4 but I had a few potato mashers and just put one in. Never thought much about it. Then I measured the voltages and did the calculations.

Forget about that rectifier chart. It's nice to get a relative performance of different rectifiers but there is no magical "fixed" voltage drop for recto tubes. The voltage drop depends on the load current and will vary from amp to amp. You know how to set bias. Just measure ***YOUR*** voltages and do the math.

[Platefire]

Thanks slucky-------yelp loose guesstimate is not good enough when dealing with one of your choice amps. I don't like pulling chassis just to get voltage. Sounds like this would be a good candidate to install the plate voltage test point right next to the bias check points like I did in my Dukane/Bassman conversion. I'll probably just let it rest until my replacement tube come in. I'm just kind of amazed at the way the amp is sounding and responding just picking around the house and was wanting to try it out with the Church Praise Band. Sometimes things sound wonderful at the house but fall apart when put with a band
I hear you talk about your Sun a lot. That must be one of your favorite amps? I only played on a Sun once or twice in my life---when my band was sitting in for a couple of songs on someone else equipment. Not long enough to truley evaluate it. From a distance they look heavy duty constructed. Platefire

[valvetones]

Max capacitance on the first electrolytic for a 5R4 is very low.
4mfd if I recall correctly.
I could be wrong , I haven’t looked at that data sheet since 2011 when I had one in my 5F6A bassman.
I remember it getting very hot.

Reading the 16 year bit, makes me think perhaps I was too timid about it.

Really whatever sounds best to you as long as your not afraid of replacing a fuse if it doesn’t work out.

[PRR]

> Max capacitance on the first electrolytic for a 5R4 is very low.
4mfd if I recall correctly.

Datasheet has no maximum. It shows 20uFd as a typical. This mostly hints what decade the tube was introduced (in late 1930s, 20uFd was "large"). With a suitable power transformer (not the beast out of grandfather's bootleg ham transmitter) you can run hundreds of uFd.

https://frank.pocnet.net/sheets/049/5/5R4GYB.pdf

[Platefire]

Well in the mean time my JJ 5AR4/GZ34($22) came in. So I have  installed it and re-set the bias. Thanks to my MX-1258/U Military Tube Socket Adapter Kit I was able to get the plate voltage without pulling the chassis.
Thanks for the info on the 5R4's. I have got three of them that says GE on the box but don't fine it on the tube. They do have a "USA" after the 5R4 GA. All three boxes have a note saying "New 1987" "Pulled in 1999". If I recall correctly, I think they came from an old local Radio Station. Long as the 5AR4's stay fairly reasonable, I'll will continue to get them. If not, I'll have these I can use. Platefire