5Y3 Vs 5AR in Ampeg B15

[boroman]

I had way too much voltages on a late 70 B15N (like 540V+ where schematic called for 450 approx) and I put 5Y3GT there that I had lying around.
I have now 490VDC, tubes biasing good, new caps, all running top. Had up to 510V in various B15Ns so 490 is okay.

The question is - is 5Y3 a cool move here? The 5Y3 will only deliver 125mA (vs 5AR4 = 50mA), also It has 2A heater (vs 3A on a 5AR4). Specs for the PT in this amp: 750vac/160mA, the amp is 3 x 6SL7 + 2 x 6L6, 25-30W RMS
I know that is calls for lower first cap (okay here), and its directly heated (which is a bit worse than indirectly in this case, but will work), but my little knowledge ends up here.
Amp sounds good.

I just need to understand it a bit more and need an info if its okay tu run it that way.

thanks!

[mozz]

Your specs are mixed up. Id be using a potato masher. 5R4.

[boroman]

Your specs are mixed up. Id be using a potato masher. 5R4.

What's mixed up here? Tried my best to explain. 5U4 can used with no problem instead of 5AR4 (and was in previous years of B15N), and 5Y3 had even more drop and should be compatible. Just checking.

[mozz]

5Y3 2A
5AR4 2A
5V4 2A
5R4 2A

5U4GB 3A.
i wouldn't run a 5u4gb unless the power transformer was spec'd to handle 3A on the 5v winding.
5Y3 running a pair of 6L6 is not common due to it being a lower current rectifier. Though some old Valcos and others did run 5Y3 but weren't pushing many watts. You get a lot of sag running a 5y3 in that bass amp.

Like i said, 5R4 is the choice here, handles higher current and will drop about 60v. They were a mil spec rectifier so should outlast everything else.

[mozz]

Somewhere out there, there is a chart showing all the 5V rectifiers, current draw, current handling, voltage drop etc.

[g1]

Also, 5AR4 can deliver 250mA, not 50mA.

[g1]

Somewhere out there, there is a chart showing all the 5V rectifiers, current draw, current handling, voltage drop etc.

Here it one (attached)

[mozz]

One more thing, the 5Y3 is rated for 125ma, You are showing the power trans at 160ma.
Second more thing, if you use a 5U4GB and the power trans burns out, you are going to have a fun time replacing it, it is a old amp. Mojotone show $350 for a power trans, why chance it.

Maybe you are good.
The PT-108 specs are primary: 117VAC 50/60Hz, secondary: 750VCT@160Ma, 5VAC@3A, 6.3VAC@5A. The measured DC resistance of one half of the PT secondary high voltage winding is 55.5 ohms. The measured DC resistance of the primary winding where the line power connects is 2.5 ohms.

[Justin Thomas]

I don't use a 5U4 in anything unless I KNOW it came that way. I'm with mozz here - 5R4 is the way to go. As far as I can tell, all varieties of 5R4 will handle high AC plate voltages & put out some good current with a good voltage drop. I actually prefer them just because they're so stout electrically.

The one and only time I tried a 5Y3 in a 2x6L6 amp (my Prosonic), the 5Y3 didn't last long...

Whatever you do, be SURE to take good care of that power transformer; replacements are STUPID expensive, possibly exceeding the cost of the amp. Maybe not that bad, but damn they're a lot.

Hope that helps!

Jusrin

[Helmholtz]

Does the PT have a 240V primary tap?
If so, use it in Germany.

What's your heater voltage?

[boroman]

One more thing, the 5Y3 is rated for 125ma, You are showing the power trans at 160ma.
Second more thing, if you use a 5U4GB and the power trans burns out, you are going to have a fun time replacing it, it is a old amp. Mojotone show $350 for a power trans, why chance it.

Maybe you are good.
The PT-108 specs are primary: 117VAC 50/60Hz, secondary: 750VCT@160Ma, 5VAC@3A, 6.3VAC@5A. The measured DC resistance of one half of the PT secondary high voltage winding is 55.5 ohms. The measured DC resistance of the primary winding where the line power connects is 2.5 ohms.

Exactly.

But 5U4 were standards in these amp up to the year when they changed from cathode to fixed bias (and 5AR4 fit then) so they raised from 25 to 30W then. I never had any problems with 5u4's but I've seen blown PTs in those amps rather frequently.

Anyway,

So if the 5AR4 and 5U4GB can handle heaters, 5Y3 too, right?
What about 160mA from the PT. I just don't get it. So, rectifier tube should have more handling than 160mA in this case? It has 125mA, so what could happen? PT stress or tube stress here?


Also, am I reading the chart above well? Max 350V? I have almost 500 here..

[boroman]

Does the PT have a 240V primary tap?
If so, use it in Germany.

What's your heater voltage?

I don't remember now. Plate voltage was not 430 as shown on the tablem, just 480+ so everything else was bit higher.

[mozz]

Well to simplify, the 5y3 is not rated high enough. If it shorts out you can burn out the transformer.

"So if the 5AR4 and 5U4GB can handle heaters, 5Y3 too, right?"
The tubes don''t "handle" heaters, they draw current to heat the heaters inside.
5AR4
5Y3 (not a choice because explained above)
They draw 2A each.
5U4GB draws 3A, will work if power transformer is rated for 3A.

You have to read what people reply and understand what they are trying to tell you. I'm out.

[Helmholtz]

The 6L6GC dataheet shows a design example for an output of 26.5W.
Total current draw at full output before clipping is 147mA. Add around 6mA for the 3 6SL7s.
The 5Y3 is definitely not suitable here (would overdissipate).
The 5R4 looks like a good choice.

[boroman]

I went for 5U4GB in the end. That was used in B15 in earlkier years (same power transformer, but theuy were cathode biased). Way less plate voltages. Running great.