Uses for Old Push Pull 6CA7 EL34 Amplifier with 600 ohm output

[tardishead]

I found one of these today at a junk shop. Old PP 6CA7 EL34 Amplifier with 600 and 300 ohm output.
It is Australian and was made for the Post Office.

It was obviously made as an amp for 100 volt or 70 volt line speakers - probably an array of them.

The output transformer is huge and really good quality. I have not tested the frequency response yet but it should be pretty good judging by the size of the thing.

If the output tranny is any good I was thinking about using this amp to drive an array of headphones for my live room.

What other uses can you think up???

How about the output for a RCA BA6A style limiter with PP EL34 output instead of PP 6V6???

 

[emrr]

use it for any limiter with 6V6, 6L6, EL34, whatever.

 

[PRR]

Mono or stereo?

IAC, an array of modern 32 ohm phones is best driven with like a few-ohm source. Put 27 or 33 ohms in series with each jack for short protection (shorts happen), wire 9 such jacks parallel, that's 8 ohms normal and 4 ohms if all-but-one are shorted.

 

[tardishead]

I use mostly Beyer DT100 which are 400 0hms per side.

 

[tardishead]

I just got round to testing this transformer.
It has a good frequency response - slight boost in the tops.

The ratio is about 1:2.4 or 600z:3500z as suited for Pentode mode Push Pull EL34. Would this be ok to use with 6v6PP - I thought 6v6 was more suited to 5k-10k output impedance?

I thought about using EL34 PP in triode mode instead to drop the power etc - but I think this is more suited to about 8k.

What about if I used it in a vari mu like StaLevel with EL34 Pentode Push Pull instead. Would this be suitable. What components would I have to change in the sidechain. Would I have to attenuate the sidechain signal?

What do you guys recommend is a good vari mu place to start. It would be a massive PP sidechain/output amp, capable of 35 watts or more.

 

[tubologic]

What about if I used it in a vari mu like StaLevel with EL34 Pentode Push Pull instead. Would this be suitable. What components would I have to change in the sidechain. Would I have to attenuate the sidechain signal?

What do you guys recommend is a good vari mu place to start. It would be a massive PP sidechain/output amp, capable of 35 watts or more.

Wow !  35 watts into 600 ohms is equivalent to a +45,5 dBm output level. Just overkill for this application.
You'll never need such a tremendous power in a compressor amp and most of this power will be wasted in huge output pads to bring down the level to a usable studio +4dBm (which is only 2,5 milliwatts into 600 ohms). In the Sta-Level and most similar compressors the side chain is driven by the final push-pull stage tube plates (at the primary of the OPT) and you don't need big power to charge a 0.1µF cap through a 6AL5 diode whose internal resistance is the main limiting factor if a very fast attack time is needed.
Using this amp for driving multiple headphones (via resistance networks to limit power) has much more sense,IMO
 

 

[tardishead]

Wow !  35 watts into 600 ohms is equivalent to a +45,5 dBm output level. Just overkill for this application.

Just because the transformer is capable of 35 watts does not mean I have to use it for 35 watts.

Many of the classic vari mu limiters like RCA BA6a, are capable of +30Dbm or more from their output amps - even the UA 175 can do +30Dbm. My desk alone can accept inputs of +24dbm at 60HZ. I am an analogue man - not strictly DAW.
I have a few killer old comps that have huge output amps and I love them. Call me wasteful in these times of "energy efficiency".

I was thinking more of a PP 6v6 output stage. The transformer has 600 and 300 ohm outputs. 3500Z load iimpedance is a little low for PP 6v6 so how about if I use the 300 ohm winding and strap 600ohm resistor across it - this will then reflect back more like a 6k load impedance back to the PP 6v6 hey????

This amp cost me $50 with some great parts - transformers like these dont come up that often and definitely not for this price.

 

[lassoharp]

Wow !  35 watts into 600 ohms is equivalent to a +45,5 dBm output level. Just overkill for this application.

Just because the transformer is capable of 35 watts does not mean I have to use it for 35 watts.

Many of the classic vari mu limiters like RCA BA6a, are capable of +30Dbm or more from their output amps - even the UA 175 can do +30Dbm. My desk alone can accept inputs of +24dbm at 60HZ. I am an analogue man - not strictly DAW.
I have a few killer old comps that have huge output amps and I love them. Call me wasteful in these times of "energy efficiency".

I was thinking more of a PP 6v6 output stage. The transformer has 600 and 300 ohm outputs. 3500Z load iimpedance is a little low for PP 6v6 so how about if I use the 300 ohm winding and strap 600ohm resistor across it - this will then reflect back more like a 6k load impedance back to the PP 6v6 hey????

This amp cost me $50 with some great parts - transformers like these dont come up that often and definitely not for this price.

Running the 6V6 as a triode?  If so Rp should be ~1950-2K.

I don't think it's wasteful - you've probably noticed the difference in sound ( esp in low end) a high current output produces compared to lower current outputs.  It makes me tend to want less compression on the signal and makes me think in terms of building those big limiter circuits as PP program amps only.

 

[takisti]

Hi,

what do you think,is the 25w output transformer enough for Sta-Level?I am on the way to order custom transformer from edcor and they offer me 25w , 8k:150ohm

 

[takisti]

and yes,do somebody have any experience with edcore transformers in sta-level?

 

[tardishead]

Can someone answer this query for me.

The transformer has 600 and 300 ohm outputs. 3500Z load impedance is a little low for PP 6v6 so how about if I use the 300 ohm winding and strap 600ohm resistor across it - this will then reflect back more like a 6k load impedance back to the PP 6v6 hey?

 

[gridcurrent]

Can someone answer this query for me.

The transformer has 600 and 300 ohm outputs. 3500Z load impedance is a little low for PP 6v6 so how about if I use the 300 ohm winding and strap 600ohm resistor across it - this will then reflect back more like a 6k load impedance back to the PP 6v6 hey?

Yes.

 

[emrr]

Can someone answer this query for me.

The transformer has 600 and 300 ohm outputs. 3500Z load impedance is a little low for PP 6v6 so how about if I use the 300 ohm winding and strap 600ohm resistor across it - this will then reflect back more like a 6k load impedance back to the PP 6v6 hey?

you may find slightly lesser frequency performance, but I expect negligible.  Just be sure to check it.