5ar4 to 5r4wgb rectifier swap ok?

[dayn]

5ar4 to 5r4wgb rectifier swap ok?

I have a Kendrick Roughneck (Champ type) amp using a 6550 output tube and the tube chart calls for a 5ar4 rectifier.

I like the sound and feel of a 5r4wgb in my Emery Sound amp - can I use the 5r4wgb safely in my Roughneck in place of a 5ar4 with the 6550 output tube?

Thanks!

[Stevem]

I am not 100 % sure until I get back to my sub book, but I do not think that will sub.
A 5v4 is very much like the 5ar4 in regards to the soft start type of think and has less voltage output and any talk of playing type sag does not take place much if any in a single ended amp like yours!

[sluckey]

I've been using this "potato masher" 5R4 with 6550s for years in my Sunn Sceptre.

[img500]http://home.comcast.net/~seluckey/amps/sunn/sunn_02.jpg[/img]

[tubeswell]

The 5V4 should handle the sub without any difficulty. You'll have more forward voltage drop (and less current supplied) than a 5AR4, but they both use a 2A rectifier winding. You may want to consider 'downsizing' the reservoir cap. A 5AR4 is a more modern design that can take 60uF at the plates, but a 5V4 is quite a bit earlier (when that typically used 8uF at the plates) so you probably shouldn't go above 22uF (although you may be able to get away with 40uF, but thats not a 'sure thing')

[Stevem]

A good NOS 5v4 will take 40uf, as I have 40 on the first node with a 5v4 in my 54 Gibson GA75 and I have been blasting it for years that way?

[pdf64]

A later type 5R4, eg the WGB mentioned, should handle a reasonably sized reservoir cap with no problem, giving similar sag as a 5U4 (ie more sag than a 5V4) whilst only drawing 2A heater current.

I suspect that the 8uF reservoir limiting value in the manufacturer's info may best be viewed in the context of the intended aerospace application for the 5R4, and that in this area, much higher line frequencies were normal, several hundred Hz. With such a high ripple frequency, small reservoir cap values would have been ample and the norm, so there may not have been any benefit for the manufacturer (and standards organisation) in determining the limiting values for a bogie tube in alternative applications.

I remember a thread on MEF in which report was given by a tech that 100 uF of reservoir capacitance on a 5R4 had no observed ill-affect http://music-electronics-forum.com/t23236/#post197328

The main concern with a modern PT though is whether the B+ winding has sufficient winding resistance; I suspect this gets overlooked as the market likes cool running PTs and is unlikely to perceive blown rectifier tubes as being due to poor PT design.

sag does not take place much if any in a single ended amp

I'm pretty sure that generally, even SE amps draw a fair bit more B+ current when cranked and so the sag characteristics of a rectifier tube type will affect the dynamic response of the amp to some degree.
From http://www.mif.pg.gda.pl/homepages/fran ... 6V6GTA.pdf it can be seen that in SE at 315VB+, the tube draws 13% more current at max signal (ie clean) compared to static conditions.
Cranked, that will rise further, though the duty cycle of the waveform will affect it.
I still haven't got around to assembling my SE amp project, so can't cite any measurements to back this up.
However, when this topic has arisen in other threads, other contributors have confirmed it.
Pete