Deacy, Maplin LT44 and LT700 and Impedance

[mac]

I bought some Maplin LT44 and LT700 while visiting London a few weeks ago.
I intend to use them in a Deacy/Mullard amp.

http://www.diale.org/deacy.html

Specs are as follow,
driver LT44: 20k:1k+1k
output LT700: 1k2+1k2:3.2

Voltage ratios are higher than those noted in the Mullard schem and others I have, mostly 3 to 1.

Possibly this transformers will work, but with higher impedance ratios, must bias adjustments be made to get the most of them 

The driver has a primary of 20k.
Is it correct to estimate the driver transistor output impedance by assuming a voltage drop across it of 9v - (some emiter and driver wiring resistance), say 7v to 8v, and then divinding by 20k to get the bias current

Same for the output transistors, almost 9v/1k2=7.5ma 

What about the driver secondaries and the base impedance 

Any help is welcome!

mac

[Kipper4]

I bought my transformers from hte chezc republic on ebay.
I had to change the legs around on the iterstage transformer as initially all i got was a noise.
A friend who made a simultanious build made the suggestion and it work.
I intend to replace them with the better transformers from the place i bought the kit at (Knight Audio technology) (not affilaited) when i have the spare money.
The cheap ones are ok but i think the others will be way closer to the real deacy sound.
I know pish about transformers so i cant help with your enquiry Mac Sorry
I hope this helps all the same
Rich

[mac]

I know these transformers are cheap, but maplin was a few block away from my hotel 

Mouser ones look better, but I have no intentions to fly to the States by now 

mac

[Kipper4]

I'm uk based.
I could have travelled 20 miles to a maplin. Instead i ordered online.
Most companys will ship world wide now and its often cheaper to shop abroad.
I wasnt having a go at the transformers. I just want to try the others. I will be gutted if i pay 3 times the price i paid just to find out they're no better.
I hope the leg swap thing helps if you run into trouble. IIRC i was getting a pulsating noise.

[PRR]

> 8v, and then divinding by 20k to get the bias current

That's an OK match for the nominal impedance you have.

It does not ensure you have enough driver power to push the output stage.

However it looks like the OT impedance is higher than the Deacy used. So it should need less drive power.

Also I suspect that what you got IS the iron for a small transistor radio, same circuit as the Deacy, but lower power (for longer battery life). Since either-way this isn't Stadium Power, you will be using it for "tone", not loudness. A bit less loudness is not a problem.

I'd run a full milli-Amp in the driver. You can afford the power, and it gives a little reserve.

[tca]

I intend to use them in a Deacy/Mullard amp.

http://www.diale.org/deacy.html

ah, you found my pages on the Deacy... I'm glad they are useful to someone!

Cheers.

[mac]

However it looks like the OT impedance is higher than the Deacy used. So it should need less drive power.

Also I suspect that what you got IS the iron for a small transistor radio, same circuit as the Deacy, but lower power (for longer battery life). Since either-way this isn't Stadium Power, you will be using it for "tone", not loudness. A bit less loudness is not a problem.

These small irons have plenty of sustain and some cream-iness, but with the speakers I'm using I'm not close to the Deacy tone.
Compared to a big 3:1 OT I wired myself Maplin OT has less power.
My hand-made iron is louder and creamy, but more like a Marshall than a Deacy 

That's an OK match for the nominal impedance you have.
It does not ensure you have enough driver power to push the output stage.
I'd run a full milli-Amp in the driver. You can afford the power, and it gives a little reserve.

If I understood you right, you mean that I should forget the nominal matching and put more current in the driver primary to have more current and power in the secondaries and bases of the output transistors?

How critical is matching transistors here?
I have a set of hfe matched ac187 and bd139 at low currents.
I'm not getting similar collector voltages,
and whenever I put excess current in their bases by adjusting base bias, one gets hot and the other cold.
I guess they should be in thermal contact, or I should match at higher currents.

ah, you found my pages on the Deacy... I'm glad they are useful to someone

BTW, Arsenio Novo circuit is great! I modded it to get the most of it, octave up included. See my gallery.

[PRR]

> hfe matched

You really want Vbe match, at some low current like 1mA.

You really want "identical" devices: same die-area, preferably from the same batch.

[Kipper4]

The Deacy is a pretty dark amp all told. Stick a treble screamer in front of it. IMO sounds great.
Did you make the direct record/headphones amp too?

[mac]

You really want Vbe match, at some low current like 1mA.

You really want "identical" devices: same die-area, preferably from the same batch.

I came to that conclusion yesterday while looking at the schematic more closely.
Until I find a Vbe matched set, I put two 10k-b pots at the bases to find the sweet spot.
I just set one to say 2k2 or so, and fine tune with the other by ear or until I get 0v from C to C.  If secondaries have the same resistance the current is almost equal in both halves.

The Deacy is a pretty dark amp all told. Stick a treble screamer in front of it. IMO sounds great.
Did you make the direct record/headphones amp too?

I have to make a live recording and/or use the pignose-like aux out.
But I have to tweak a little more.
And plug my RM

mac

[mac]

With due respect to Mr Deacon and Mr May, I recorded a quick sound demo using Maplin transformers and two parallel 4" x 8 ohms small Aiwa cabs.
Breadboard background motorboating included 

http://www.aronnelson.com/gallery/main.php/v/mac/sound+demos+of+my+circuits/waltz.mp3.html

I'm breadboarding using 4 x AC187. I modded the output pair bias by using a fixed 2k7 at one base, a 5k-b pot at the other base to adjust bias current at both halves of the transformer, and a 100 ohm pot instead of the 39 ohm.
The transistors are slightly warm @ 7v.
The rest is similar except for a 4k7 between the 1st and 2nd stages.

Not so bad for 4.98 pounds 

mac

[Kipper4]

Samples would be good please

[MAPRIDEL]

HELLO, I'm writing to you because I'm riding a deacy amp.
I have the lt44 and lt700, but I'd like to mount the plate with the original transformers.
you could pass me the link to buy them.
many thanks and greetings

[mac]

I have the lt44 and lt700, but I'd like to mount the plate with the original transformers.
you could pass me the link to buy them.

I'm not sure if the guy who discovered that the Deacy circuit was a Supersonic PR80 radio made in Zimbawe in the 60s, or a clone of it in the UK, sells transformers similar to the originals.
I have the schem of that radio. The output transformer is not similar to Maplin or Mouser ones. Looks like an auto transformer.

mac