Is there a way to measure the amount of supply current in the 2nd tabs of the Power Transformer?

[psychepool]

When I make an amp, I don't make a 1:1 copy of a specific model, but I make it by omitting or modifying some parts, so I order and use the Power Transformer from the local shop as the necessary specifications.

If I mention the list of tubes or ICs that go into the amplifier I will make, the shop makes the trans with the specs on its own.
The reason for order like this way was that I thought it would be safer because I'm not the one with the exact knowledge of electricity.

But I haven't asked about the exact supply current specification while ordering transformers there.
I haven't felt the need for it because I've been building well with the transformers I ordered there.

However, I recently thought that I would like to replace the power tube of my amp with another one.
I'm currently using 6L6 pair and I want to replace it with EL34 or KT77.
It's a generally problem-free condition to use EL34, but maybe heater current is a problem. There was a significant difference in heater current consumption between the two. Since it is 6L6 : 0.9A / EL34 : 1.5A, a difference of 1A or more occurs when the pair is replaced.

I'm hesitant to replace the tube because I don't know the exact supply current specification of the power transformer I'm using.
Even the ordered company doesn't seem to have a list of them all. Because my order is like a small dot in a large number of bulk orders.

Is there a way to check the supply current specification of the Power Transformer 2nd tab?

[Stevem]

Let's look at the numbers.

Four 9 pin preamp tubes need 1.2 amp of heater current, then add to that another 1.8 amps for the heaters in the 6L6 type tubes for a total of 3 amps.

NOW

Take the at same 1.2 amps of preamp tube current and add the 3 amps needed for the 34s and your needs are now 4.2 amps total.
A power transformer that was happy providing 3 amps with maybe a tad to spare is going to flat out burn out when asked to provide 40% more heater current

This is how it's done, not the way your thinking of doing it.

[pdf64]

The transformer was designed to cope with 6.3x3= 18.9VA load on that winding.
There might be another 150VA load from the HT winding?
The total max load might be 170VA.
You're wondering whether it'll cope with increasing the heater winding load to 6.3x4.2=26.5VA.
The total max load might then be up near 180VA.

So from the perspective of the primary winding and magnetic core, it's probably not a big deal.
It also seems probable that if the the magnet wire used for the heater winding was fine for 3A, it would probably cope with 4.2A.
The only concern I have is that a hot spot might conceivably develop within the winding coil.
I suspect only the designer of the transformer has sufficient info and competence to determine that.

I suspect it would be fine.
I suggest to use a thermocouple etc to identify the hottest accessible part of the transformer surface, put the amp in its cab and run the amp at full power for an hour with 6L6, note the transformer temperature, then fit EL34 and monitor the temperature at idle for 30 minutes, then 1/4 power for 30 minutes, etc.
If it runs at full power at pretty much the same temperature, it'll probably be ok.

[martin manning]

I'd consider I^2R for the increase in localized heating of the heater coil, which would be (4.2/3)^2 = 2x.

[oxbow_lake]

I'm not an expert so apologies if this is already common knowledge or not applicable. Maybe useful?

In Gar Gillies' tube amp book he offers a way to estimate the current rating for a high voltage winding.
1. Measure the resistance of 1/2 of the high voltage winding.
2. With the winding unloaded, connect the primary to the mains. Measure the voltage across half of the secondary. There is the obvious risk of shock here.
3. Divide the voltage on half the secondary by the resistance of half the secondary, then multiply that by 25 to arrive at "a reasonably accurate current rating for the high voltage winding." He says it's accurate up to 200mA.

Like I said I'm not an expert and this could be totally wrong. Also not going to be useful for the heater winding.

[psychepool]

Thank you for your all reply. At my level of knowledge, I don't think there is anything I can easily understand or try.

Because I always do tight builds, if there is a problem with the transformer, I have to dismantle all the internal parts to replace it with a new one, so I am careful.

Using EL34 in its current state seems like a gamble. Actually, I'm not dissatisfied with the sound of the current amplifier, and the purpose of replacing the tube was just curiosity, so I just played it safe and continued to use the 6L6.

[Stevem]

The main difference you would find with 34s is that the output stage will clip sooner .

34s have more gain then a 6L6, and of course this also translates into a tad more touch sensitivity.

This may help to float your boat or maybe not?

One other thing you can try is a set of Groovetubes 6L6 tubes .
There can be had in a range of ratings from 1 to 10.
A number one will clip early and a number 10 will clip late.

Also a number 10 will be a tad louder and punchier then a number 1.

A number 5 is considered average.