lundahl ll1660/s for phase invertion/splitting

Am getting impatient, got an ST70 with the original board, bass sounds too flabby in my system.

I live in Asia, driver board upgrade is a few weeks away.

Am thinking of removing the stock driver board, install an aluminum plate with two 9 pin sockets and a pair of Lundahl 1160s/10ma. I will use a pair of 5842 as voltage amplifier.

5842 operating point is 186V on plate, 20ma per tube.

Any thoughts?

just my own opinion of course, but #1 that's a huge amount of money (unless you've already got the transformers)
and #2, that's an awfully lot of extra current draw on the power supply!

I already own a couple of pairs of lundahl ll1660.

On the stock configuration, how much current does the 7199 draw? How much current is allowed for a preamp to be drawn from the octal sockets on the front of the ST70?

I throttled down to about 15ma per 5842, sounds excellent!

I just experimented with this as I will be ordering the VTA board on Monday. It was also an opportunity to test the 5842 driver and lundahl 1660, I will be building an EL34 PP amp with these. Besides the ll1660 looks awful on the ST70 chassis.

I had to look at the Dynaco manual to answer your questions.
The schematic and voltage charts don't list voltage or current for the 7199, most likely because those tubes have so much variation in production quality. You can measure across the two 47K resistors on each 7199 to calculate the current (I=V/R ohms law) for the phase inverter half, and across the 270K resistor for the voltage amp. Filament current is 450ma each.
The preamp output sockets are rated at 6v 1 amp for filaments and 350v 10 ma for B+

tubes4hifi wrote:I had to look at the Dynaco manual to answer your questions.
The schematic and voltage charts don't list voltage or current for the 7199, most likely because those tubes have so much variation in production quality. You can measure across the two 47K resistors on each 7199 to calculate the current (I=V/R ohms law) for the phase inverter half, and across the 270K resistor for the voltage amp. Filament current is 450ma each.
The preamp output sockets are rated at 6v 1 amp for filaments and 350v 10 ma for B+

So am safe on the heater current and a few ma over on the HT.

Anyway, this is a temporary experiment, I will order the VTA board and proceed from there, and I will build another PP EL34 using the Lundahls as they sound so good in the midrange and highs driving my Opera Seconda.

the 5AR4 rectifier is rated at 250ma, so it's probably safe to run at 200ma total B+ draw.
If the four output tubes are only biased at 40ma each as I recommend, then you've got 40ma left over to play with.
The VTA70 driver board uses about 17ma total. The new octal board uses about 25ma total.
Anyone trying to run KT88s at 50-55ma each is already pushing their luck and should probably use the Weber SS replacement along with the time-delay-relay board.