5R4GY longevity in tube amps

[Mick Bailey]

I rediscovered a few NOS Tung-Sol 5R4GY rectifiers rated at 250mA at 750v, but the maximum 1st filter cap is listed as 4uf. How do these hold up at half of the voltage/current but into a typical 20uf filter cap?

My thinking is that the cap size is given for the maximum voltage and current and it may be safe to increase the cap size if both these are lower. I've only seen these in radio transmitters and not come across them in amps. Anyone use them?

[pdf64]

I recall a similar thread in which Enzo mentioned that he had 5R4 info with a higher reservoir cap limit.
A key thing may be to ensure that there's sufficient resistance in the plate circuit so as to limit current.

[Mick Bailey]

Ah, just spotted that. Thanks. Looking through the spec sheets it appears that the 'max' cap value gets reworded to 'typical' in the later sheets. But the typical scenarios are using much higher voltages than found in tube amps - between 1400v and 2000v plate-to-plate at 250mA.

[pdf64]

For the few I've dealt with, I've just subbed them for GZ34 without any problem, even with 50uF reservoir cap.
KCA seem to endorse that approach, though I wonder if failures under such use would be granted a warranty replacement https://www.kcanostubes.com/content/...ifier-swapping
They seem to give a saggier result than might be expected, I think a Super Reverb's output was brought down to about 25W with a 5R4, compared to around 40W with a current production 5AR4.

[Tom Phillips]

...They seem to give a saggier result than might be expected, I think a Super Reverb's output was brought down to about 25W with a 5R4, compared to around 40W with a current production 5AR4.

I think there must have been something else in play to cause such a large power difference. The voltage drop across a 5R4 vs. that across a 5AR4 wouldn't account for that unless the sample 5R4 was faulty.

[pdf64]

I've been using Philips ECG USA JAN 5R4GA, which all seem to have similar performance.
A similar degree of sag at full load to 5U4, which again is more than I expected.
What results does anyone else get, ie comparing amp power output using GZ34 and then to various other rectifier types?

[ron vogel]

I've been using Philips ECG USA JAN 5R4GA, which all seem to have similar performance.
A similar degree of sag at full load to 5U4, which again is more than I expected.
What results does anyone else get, ie comparing amp power output using GZ34 and then to various other rectifier types?

You mean this?:
http://music-electronics-forum.com/t34626/

[Mick Bailey]

The voltage drop for a rectifier is given at maximum output so the actual drop can be quite different in an amp.

For instance, a 5Y3 (60v drop at 125mA) gives a greater drop in a 5E3 than a 5R4GY (67v drop at 250mA).

[stokes]

As to the original topic,longevity of the 5R4 with increased input cap value.I've got JAN/Phillips 5R4's in a couple of amps I've built for my sons,one has an 80uf and the other 100uf as the input caps.They've been working fine for 3-5 yrs,and they see a lot of use.

[okcrum]

As to the original topic,longevity of the 5R4 with increased input cap value.I've got JAN/Phillips 5R4's in a couple of amps I've built for my sons,one has an 80uf and the other 100uf as the input caps.They've been working fine for 3-5 yrs,and they see a lot of use.

The RCA tube manuals say you only need to increase the circuit impedance when using more than 40 uf at the filter input for best tube life.