redplating 1959 w larmar

[raiken]

Randall,

the OT should be 1k7. can I use 9-12v AC or is that too high?
I'm really abusing a pair of RTF el34s and one pair of new gold lion kt88s now and can get absolutely no redplating on the kt88s even with hot bias and punching riffs for 15minuttes. one RTF started to redplate after 15minutes with 65% bias.

b+ went down to 473v with hotter bias
my mass150 have never been this hot before - thats for sure.

No, you can't use a battery, it has to be an AC source.

The KT-88 is a 42W tube, whereas the EL34 is a 25W tube. You can run the KT-88 at 3.4K (1.7K) and 480V at up to 65mA idle, or up to a whopping 73mA at 473V without exceeding the dissipation ratings.

RA

[Roe]

Sorry, I was messing a little here.

After double checking these are the values:

No load connected to OT.
10.25 ac applied to primary
16 ohms secondary - 2.02v
8 ohms: 1.44v
4 ohms: 1.03v

EDIT: measurement turned out to be wrong, one of the wires connected to one of the plates must have touched another pin

With 13.1ohm load connected:
10.3V AC on the PRIMARY gives the following voltages:
16ohms secondary with a load that measures 13.1 ohm: 1.73v
8ohms secondary with a load that measures 13.1 ohm: 1.32v
4ohms secondary with a load that measures 13.1 ohm: 0.99v

sorry for the confusion. all of these measurements were with tubes installed

[flemingmras]

10.2V AC on the PRIMARY gives 2.02V on the 16ohms secondary

That doesn't sound right. Are you hooking up the signal generator from plate to center tap? If so it needs to get hooked up from plate to plate (i.e. plate of V4/V5 to plate of V6/V7).

Now if that was in fact a plate to plate measurement, that's WAY too low.

[Roe]

10.2V AC on the PRIMARY gives 2.02V on the 16ohms secondary

That doesn't sound right. Are you hooking up the signal generator from plate to center tap? If so it needs to get hooked up from plate to plate (i.e. plate of V4/V5 to plate of V6/V7).

Now if that was in fact a plate to plate measurement, that's WAY too low.

yes, that was measured with 10.2v between the plate to plate, something which reduced in 2v on the 16ohms secondary

[flemingmras]

10.2V AC on the PRIMARY gives 2.02V on the 16ohms secondary

That doesn't sound right. Are you hooking up the signal generator from plate to center tap? If so it needs to get hooked up from plate to plate (i.e. plate of V4/V5 to plate of V6/V7).

Now if that was in fact a plate to plate measurement, that's WAY too low.

yes, that was measured with 10.2v between the plate to plate, something which reduced in 2v on the 16ohms secondary

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

[Roe]

...
yes, that was measured with 10.2v between the plate to plate, something which reduced in 2v on the 16ohms secondary

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

I just connected an AC power supply to the plates, something which resulted in 2v between the 16ohms secondary (and the common on the secondary's side)

[flemingmras]

...
yes, that was measured with 10.2v between the plate to plate, something which reduced in 2v on the 16ohms secondary

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

I just connected an AC power supply to the plates, something which resulted in 2v between the 16ohms secondary (and the common on the secondary's side)

OK in that case, measure BOTH the primary AND secondary voltages while the supply itself is connected to the primary of the transformer. Your supply voltage more than likely drops some when hooked up to the primary so you need to measure your supply's output voltage while it is connected to the primary.

[Roe]

..

After double checking these are the values:

No load connected to OT.
10.25 ac applied to primary
16 ohms secondary - 2.02v
8 ohms: 1.44v
4 ohms: 1.03v

...

this gives the following impedance ratios:
16ohms: 25
8 ohms: 50
4 ohms: 99

This suggests that the Z is only 400 ohms

[Roe]

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

I just connected an AC power supply to the plates, something which resulted in 2v between the 16ohms secondary (and the common on the secondary's side)

OK in that case, measure BOTH the primary AND secondary voltages while the supply itself is connected to the primary of the transformer. Your supply voltage more than likely drops some when hooked up to the primary so you need to measure your supply's output voltage while it is connected to the primary.

I double checked and its pretty stable at 10.2-10.3v. I'm using the voltage supply for a line6 dl4 delay pedal, a pedal that requires quite a bit of power

should I remove tubes when measuring?

[flemingmras]

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

I just connected an AC power supply to the plates, something which resulted in 2v between the 16ohms secondary (and the common on the secondary's side)

OK in that case, measure BOTH the primary AND secondary voltages while the supply itself is connected to the primary of the transformer. Your supply voltage more than likely drops some when hooked up to the primary so you need to measure your supply's output voltage while it is connected to the primary.

I double checked and its pretty stable at 10.2-10.3v. I'm using the voltage supply for a line6 dl4 delay pedal, a pedal that requires quite a bit of power

should I remove tubes when measuring?

Not really necessary but make sure that the amp is off obviously.

But yeah with your numbers 400 ohms is exactly what I got too, which is WAY off from the 1k7 that it's supposed to be plate-plate and as such WAY too low.

Really stupid question, but that power adapter that you're using has an AC output, not a DC output correct?

[raiken]

Are you sure you've got your OT wired correctly (and connected correctly for the test)? You should have around 425 ohms on each side, with 1.7K from plate-to-plate. If you're measuring one side, that sounds about right.

RA

[Roe]

OK...with the generator hooked up to the transformer under the load of the transformer, do you measure 10VAC from V5 pin 3 to V6 pin 3?

Also, what is your test frequency?

I just connected an AC power supply to the plates, something which resulted in 2v between the 16ohms secondary (and the common on the secondary's side)

OK in that case, measure BOTH the primary AND secondary voltages while the supply itself is connected to the primary of the transformer. Your supply voltage more than likely drops some when hooked up to the primary so you need to measure your supply's output voltage while it is connected to the primary.

I double checked and its pretty stable at 10.2-10.3v. I'm using the voltage supply for a line6 dl4 delay pedal, a pedal that requires quite a bit of power

should I remove tubes when measuring?

Not really necessary but make sure that the amp is off obviously.

But yeah with your numbers 400 ohms is exactly what I got too, which is WAY off from the 1k7 that it's supposed to be plate-plate and as such WAY too low.

Really stupid question, but that power adapter that you're using has an AC output, not a DC output correct?

ok, so its not necessary to take out tubes while measuring

if this OT has a low Z that could explain a few things

[Roe]

Are you sure you've got your OT wired correctly? You should have around 425 ohms on each side, with 1.7K from plate-to-plate. If you're measuring one side, that sounds about right.

RA

its wired according to the colour codes metro/heyboer provides.

could it be that the CT and one of the plates have got mixed by heyboer?

edit:
measured between CT and either plate I got the following voltages of the secondary when 10.4v was applied to the primary:
16: 1.98v
8:1.41v
4:1.00v

[raiken]

Are you sure you've got your OT wired correctly? You should have around 425 ohms on each side, with 1.7K from plate-to-plate. If you're measuring one side, that sounds about right.

RA

its wired according to the colour codes metro/heyboer provides.

could it be that the CT and one of the plates have got mixed by heyboer?

No, I don't think so, because you would get a very weird output signal. Measure both sides, from CT to each side, and then from one side to the other and see what all the measurements are. The other possibility is that the transformer has poor response down at 60Hz, and you may need to use a higher frequency to measure.

RA

[Roe]

Are you sure you've got your OT wired correctly? You should have around 425 ohms on each side, with 1.7K from plate-to-plate. If you're measuring one side, that sounds about right.

RA

its wired according to the colour codes metro/heyboer provides.

could it be that the CT and one of the plates have got mixed by heyboer?

No, I don't think so, because you would get a very weird output signal. Measure both sides, from CT to each side, and then from one side to the other and see what all the measurements are. The other possibility is that the transformer has poor response down at 60Hz, and you may need to use a higher frequency to measure.

RA

measured between CT and either plate I got the following voltages of the secondary when 10.4v was applied to the primary:
16: 1.98v
8:1.41v
4:1.00v

between the plates I get the following:
16: 2.02v
8: 1.45v
4: 1.03

edit: I double checked w/o tubes and got the same values.
AC should be 50hz here btw