18w OT

[TIMBO]

Hi guys, Same 18w amp as the other thread.....
It seems that this was a kit of sorts...
The supplied OT has clearly marked that it has a 4k primary and the best calculation I can get is about 3.5k
Data sheets says 8k best load and most 18w OT are 8k
I know I can get a ballpark secondary impedance by putting the 8ohm on the 4ohm tap etc. but this will leave one notch on the impedance selector without a connection to the ot.....
Is 4K too low for a pair of EL84s

[sluckey]

Is 4K too low for a pair of EL84s

I think so.

[Latole]

Pair of EL84 need 8 to 10 K ohms

[kagliostro]

3.5K .... perfect for a pair of ...... UL84 - Class AB 13W ..... but only @ 170V B+

https://frank.pocnet.net/sheets/030/u/UL84.pdf


Franco

[Latole]

3.5K .... perfect for a pair of ...... UL84 - Class AB 13W ..... but only @ 170V B+

https://frank.pocnet.net/sheets/030/u/UL84.pdf


Franco

And a pair of 6V6, 6L6, EL34, KT88 and more.

[sluckey]

And a pair of 6V6, 6L6, EL34, KT88 and more.

It's more common to see 6V6s working with 6K to 8K. Don't think I've ever seen a pair of 6V6s running at 4K.

[Latole]

Hammond 1615, 1645 at 5K can drive 6V6s

[kagliostro]

Don't think I've ever seen a pair of 6V6s running at 4K

I think you did, but didn't recognized it

I'm kidding: icon_biggrin:

if I'm not wrong, there are 6V6 on a 4K load on the Mesa Blue Angel, but that is all an other particular affair



Franco

[sluckey]

Hammond 1615, 1645 at 5K can drive 6V6s

You were talking about 3.5K

[mresistor]

 4K load on the Mesa Blue Angel

Franco I'm pretty sure the Blue Angel OT has 5K primary.

[shooter]

I'm in the 8K crowd, but if it's self biased, going to 4K won't risk as much as fixed bias, sound_wise, all bets are off

this will leave one notch on the impedance selector without a connection to the ot

for "safety" you can just jump it to a "valid tap" and just have something like 8,16,16

[dude]

4K impedance too low for an 18 watt OT, more like 8K is the norm.  Like you said, you could use a higher ohm spk on the tap, double what it calls for but l'll get the correct OT for that amp.

[kagliostro]

Franco I'm pretty sure that the Blue Angel OT has a 5K primary.

mresistor if you are really sure, it is very welcome information

Years ago I did a search on this on the Web and, at the time, the guessed conclusion was that it would be 4K

So if yours is secure information (reverse engineering on the OT), I'm very happy to have it

Many thanks

Franco

p.s.: I apologize for the OT

[TIMBO]

Thanks guys, A new OT is the go, unfortunately they are a bit hard to find at the moment.

[2deaf]

Is 4K too low for a pair of EL84s

You can get 18W out of a pair of EL84's with an 8K load and still remain within the maximum ratings.  You can also get 18W with a 3.5K load, but the plates would have to be 320V and the screens 315V.  The EL84's will be up to twice the maximum dissipation for much of cycle.  If you want the EL84's to operate within the maximum ratings with a 3.5K load, you're going to be hard pressed to get much more than 6W.