Push-Pull from Stereo SE amp

[benproiii]

I was recently given a RCA New Vista Victrola console amp chassis. It has two EL84's and is in single ended stereo configuration. I was wondering if it was possible to make it into a mono push-pull amp. Like this:

run the tubes with a standard phase inverter and connecting the secondary's of the transformers together. is that possible or do you have to use one OPT for push-pull.

[rojoknox]

Greetings from FixitLand!

You will need a proper push-pull output transformer. The characteristics of PP and SE transformers are such that they are not interchangeable. A Hammond 1608 (8KCT) or 1609 (10KCT) would work well. I used 1609s on my EL84 amp.

Take care,
--
J. E. Knox "The Victor Freak"

[DigitalJunkie]

Hmm,well each SE transformer is gapped,to handle the DC,so that shouldn't be an issue?
You'll have to mind the phase of the output trans. secondaries,so they're both in phase.
Or perhaps connect the secondaries in 'anti-series'. for a sorta bridged output. -(basically grounding the neg end of each 8ohm winding,and connecting the load/speaker across both + output terminals)

At the moment I can't see any major reason why it shouldn't physically work? (Anyone see anything?)
How it will sound is anyone's guess. Might be interesting for a guitar amp!?

[DF96]

For best push-pull you need tight coupling between the two halves of the primary. You won't have this. It might work, but not as well as a real p-p. Also, you will need a 4 ohm speaker to provide the correct load as both valves are driving it in parallel so each see half the load.

A lightly-loaded SRPP with low mu valves might give you slightly higher distortion than a simple grounded cathode with active load (i.e. take output from lower anode instead of upper cathode) but the difference will be small. SRPP is good for its particular purpose, but no advantage otherwise.

[benproiii]

I'm thinking of running the tubes and OPT's in parallel for more power, how much power does a parallel SE EL84 amp make.

[TheGimp]

You can parallel them or you can bridge them (Series). Either way you will get about twice the power out. Parallel should drive a speaker with half the immpedance, bridge should drive one with twice the impedance of the original.

In the schematic shown you are set for 8 ohm speakers. optimally you would want to drive 4 ohms in parallel and 16 ohms in bridge (series).

I would expect parallel to produce twice the power of the single se which is around 3-5W for the EL84. So you will get around 6-10W which is about half of what you will get with a properly designed PP amp with EL84s.

[Miles Prower]

http://www.diyaudio.com/forums/attac...be-amp-ccs.png

It's a slick idea. Unforch, it only works for RF amps with air core OPTs. Otherwise, it's not gonna work since the two halves of a proper PP xfmr need to be coupled as tightly as possible. It's not like two xfmrs on the same core, and you can't separate them like that.