My first amp was a... Deacy!!!

[mac]

I was experimenting with those tiny LT700/LT44 output/driver transformers when I remembered my old japanese Crown CRC 530SW radio which was my first amp when I was, how old... 5 or 6 ?
I used to plug my first guitar in the mic input of a Pioneer Centrex KH 7766 and played clean... as you can imagine, it was too boring for a very young juvenille.
But one day I connected the headphone output of the Pioneer to the aux input of the Crown, disabled speakers, set the radio to record and monitor, cranked  heaphone volume and voila... distortion!!!
That's the day my father had his first heart attack

I played with it for many years. It had a nice and sweet sound for what it was. And the day I heard Queen for the first time I noticed it sounded in some ways similar to Brian's Deacy.

I found it at mother's all covered in dust. I powered it on but there was no sound. I surely did some butchery to it long long ago
Instead of trying to fix it, I opened it and as I guessed it had two lovely audio transformers a la Deacy.
I took some pictures, followed the circuit as far as possible and measured voltages here and there. Then I gently removed the transformers to clone the circuit in the breadboard.

Here it is, another old radio Deacy-like circuit that sounds pretty good and loud when driven with another source,



More images of its guts in my gallery.

Some points marked with a ? go to a complex radio to tape, aux/mic in monitor, headphones, remote, etc, multi-switch. I drew the power section and what I think is the radio detector or something.
The points marked as ?? could be a negative feedback path from speaker.

Output transformer has a second secondary 90 ohm winding which I think it is used for headphones.

I have the transformers in the breadboard right now. It's connected to my Laney 12" speaker. It is very loud, like my Valve Jr, and I had to heathsink both BD237. I don't know how those D355 survived the heat, if any. Maybe the strange diode D11 does something. Or the poor on-board speaker does not let the output transistor heat too much. I hope to clone the sound with a cheap mid speaker and a booster like I used to do with the headphone output of my Pioneer stereo.

Enjoy,

mac

[tca]

> Maybe the strange diode D11 does something
That is a diode temperature compensating diode and it should be mounted near the output transistors, with the resistances (can't read the labels on that) minimizes cross-over distortion. Those transformers depends on the BJT specs, need to do some more math to give a complete answer. Didn't  get if you are using the original transistors and transformers.

Cheers.

[tca]

From your gallery it seems that it runs on 6V?!?
What was the voltage that you used? I'm seeing some 7.1V in your schem, probably, and partially, that explains the temperature of the BD237s.
ah, that is an output voltage isn't it?

[mac]

That is a diode temperature compensating diode and it should be mounted near the output transistors, with the resistances (can't read the labels on that) minimizes cross-over distortion.

Actually it is... was glued to the driver transformer 
I've just realized that Pignose 7-100 uses a diode and a 220 resistor too.

Those transformers depends on the BJT specs, need to do some more math to give a complete answer. Didn't  get if you are using the original transistors and transformers.

I didn't post the DC resistances of the OT because they are very small, much like the ones in the Mullard schematic.
I bet it is 3 or 4 to 1.
D355 hfe can be calculated as (15.5mV/1ohm/2)/(1.8mV/14.9ohm) = 65
C711 gain is, from Q13 data, (0.178V/0.150K)/{(2.65V-0.812V)/390K} = 251

I searched datasheets on the web, it seems these are Mitsubishi 2SC711 general purpose, and 2SD355 800mw, 1A in a bigger TO92 case than say 2N3904.

I'm using both transformers, and BC550B of similar gain to those C711, and BD237 that have a gain of 80.
I cut two 2.5cmx2.5cm pieces of zinc sheet as heathsinks.
Voltage from my 9v supply.
The power sections runs at 9V, and the rest is at 7v.
Massive sound through a 12" speaker.
I have to use another supply and a small speaker to check temperature of the power transistors.

From your gallery it seems that it runs on 6V?!?
What was the voltage that you used? I'm seeing some 7.1V in your schem, probably, and partially, that explains the temperature of the BD237s.
ah, that is an output voltage isn't it?

The CT power transformer put 7.1v on the circuit.
It also have a 6v DC input, and it can run from 4 batteries.

Since it's not working, and now without the transformers, I did not have the chance to test the output transistors temperature when driven hard. But after many years of abuse I guess they ran close or below the power limits.

mac

[Jdansti]

Sorry I can't help, but you reminded me of my dad's old Pioneer amp that I used to play through before I had a real guitar amp. He had nice, but under rated Acoustic Research (AR) speakers connected to it, but we always made sure we didn't play records or the tuner too loud to avoid damaging the speakers. One day I accidentally plugged the cable into my guitar with the amp's volume control set too high and the pop blew both speakers. I was in the dog house for a long time after that!

[mac]

I was in the dog house for a long time after that!

I was there so many times too that I find Purina Dog Chow really tasty!

Acoustic Research (AR) speakers

My father bought that Pioneer with a pair of Philips 10" two way speakers still in use and looking great.
It was my mother who oftenly blew speakers listening to Beethoven 9th or Brahms 1st 

mac

[Jdansti]

Funny memories!  

My mom and I unintentional warped a stack of my Dad's Chicago albums (from the Terry Kath era). I spent most of a Saturday listening to about seven or eight Chicago albums and left them in their sleeves lying on the floor. I also left the Dynaco tube amp on. Mom cleaned up after me and placed the stack of albums on top of the amp. Dad found the warped albums the next day. Mom and I were both in the dog house and I got it double because Mom was mad at me too.