Foreplay 1 with 7193 tubes

[armindillo]

Hi

In January 2000 I bought an Electronic Tonalities Foreplay kit.
It sat in its box until about 2 weeks ago, but now I have a working preamplifier.
I'm pretty sure it's the messiest assembly and soldering job anyone ever did, but it works!

The top side looks just as sketchy as the underside.

Before building it I became charmed by the crazy look of the 7193 tubes and the internet says they sound great so I felt I had to use them.
I ordered 4 tubes and 2 adapters in ebay and was warned by the manufacturer of the adapters that they require 6.3V.
All I did was wire the heater connections of the 2 tube sockets in series and indeed that seems to work.
(In each socket, terminals 4 and 5 are connected and terminal 9 is connected between both sockets. The two 12.6V power cables each go to one of the 4=5 terminals.)
Other than that it's stock, with the anticipation and whispers upgrades.
Right now each tube adapter is sitting on a tower of 2 socket savers to clear the RCA connectors. Once I get some right-angle connectors all I need is a single socket saver on each side to clear the knobs and connectors.

[armindillo]

My attempt to post a photo:

[Thermioniclife]

7193/2c22, 6j5's and e1148 tubes are similar and cool, pretty much 1/2 of a 6sn7 or 12au7.
here are a couple of preamps I built based on the Foreplay III platform.

[Paul Birkeland]

Two 7193s draw as much heater current as two 12AU7s, and I am remembering that the power transformers on the Foreplay I and II didn't have much to spare.  You have four 7193s on there, so I would expect relatively short life from the power transformer running under those conditions.

[armindillo]

Yes, I've seen other warnings in the forums about overloading the transformer.

Before the adapters arrived I also tried some 12BH7 tubes which sounded really good but have the same increased heater current.

I'll look into getting a more powerful transformer. When I do that should I look for one that puts out 6.3V and heat the tubes in parallel or am I ok with the serial 12.6V arrangement?

[Thermioniclife]

Ask Queen nicely and she may sell you a PT-10. Witch can carry that heater current.

[Paul Birkeland]

A PT-10 would definitely power the circuit, but I don't know how you'd fit it on the chassis plate and those old plates are very thin aluminum since there isn't much weight mounted to them.  It might be possible to mount a second power transformer and make the circuit dual mono, which would add enough headroom to deal with the heater current problem.  I suppose you could also add a 12V/2A power transformer to just heat the tubes.

[armindillo]

Thanks Lee and Paul

After a bit of web searching I found that Edcor can make a 125V@40mA / 6.3V@2A transformer. It takes a while to be made but I hope my current transformer survives for a while.

Another option (quicker cheaper, uglier) is to add a 6.3V transformer for just the heaters.

Seeing Lee's beautiful preamps inspires me to go with the Edcor.

[2wo]

Another possibility would be a 12V "wall wart". That would solve the mounting problem...John

[Thermioniclife]

I think a 12 wall wort would not be appropriate as the heaters require 6.3 Vac or Dc. a 12Vac center tapped transformer would be more appropriate. you could mount said trans on the wood base with dissamble connectors to make it easier to dissemble. I forgot to include a pic of the Faux play III that a nice fellow from Washington State sold me an original Foreplay III extended kit to me. Thank's you know who yuo are.

[armindillo]

the heaters require 6.3 Vac or Dc

In my setup with the adapters for the 12au7 socket I can use 12.6V or 6.3V and currently the 12.6Vac Foreplay1 transformer is doing the job. With a 6.3V supply I can put different tubes in the right and left channel and do some side-by-side comparisons so I prefer 6.3V.

It might be cool to try an external 6.3Vdc source but I am not getting much ac hum at the moment so it would probably sound the same.

[Paul Birkeland]

It might be cool to try an external 6.3Vdc source but I am not getting much ac hum at the moment so it would probably sound the same.

Powering your heaters with a wall wart is a good idea and suitable workaround for the extra heater current you need.  Just put the preamp and wall wart on the same power switch and use that to switch them both on at the same time.

[armindillo]

I bought a 6VDC@5a power supply. I realized that with 5 amps available I can even try out 2C26 tubes which have heaters that draw 1.1 amps.
The multimeter reads 6.3V for the new power supply. The power supply even has a power cord so it is easier to plug in than a wall wart.

So far so good! I managed to get it hooked up and am listening to music with the new power supply and the 2C22/7193 tubes.

However, things are not perfect. Due to my atrocious soldering skills I temporarily shorted socket terminals 8 and 9 and blew out one of the LEDs on one of the anticipation boards. For now I took out that board and replaced it with the resistor from the original design.

I see that they sell LEDs on this site. They look different from the one I broke, but will one of those work on the Y2K anticipation board? The manual just identifies it as "H-P special Light Emitting Diode".

[Paul Birkeland]

I ended up with the surplus supply of those diodes some years ago.  If you PM me your address, I can mail you a couple.

[armindillo]

Thank you Paul!

I really like the 2C26 tubes.
When using all 4 tubes, the 2C22 tubes were generating some hum that would disappear when I touched the wire to the top cap.
The 2C26 tubes do not have that issue. They have a bit less gain so I turn up the volume a bit but I think they sound really nice and clear.
Those tubes are also really cheap because nobody has any use for them.

Here is a picture that shows the added input from the 6VDC power supply: