Deacy Amp (?)

[greaser_au]

Hi.  Could you please share the links for the Mullard and the KAT?

Nick,

In addition to my earlier comment, the Mullard 1W amplifier schematic appears on page 171 of the "Mullard Reference Manual of Transistor Circuits Mullard Ltd 1st ed 1960" (I was able to find a PDF download quite easily).

david

[mac]

I bought those LT44/700 transformers from Maplin in the UK. IMHO they are too small for this circuit. They work but the output transformer impedance ratio drops a lot of volume.

If you ask me, I'd buy old radios from the 60s with bigger transformers. You could remove the transformers or, if the radio has an AUX input, you can overdrive the input with a TS or RM or whatever.

That's what I used to do when I was a little kid, I pluggled the guitar into the MIC of a Pioneer stereo, and pushed the AUX input of an old Crown radio recorder via the headphones OUT. See my gallery.

mac

[Rob_Lo]

I bought those LT44/700 transformers from Maplin in the UK. IMHO they are too small for this circuit. They work but the output transformer impedance ratio drops a lot of volume.

If you ask me, I'd buy old radios from the 60s with bigger transformers. You could remove the transformers or, if the radio has an AUX input, you can overdrive the input with a TS or RM or whatever.

That's what I used to do when I was a little kid, I pluggled the guitar into the MIC of a Pioneer stereo, and pushed the AUX input of an old Crown radio recorder via the headphones OUT. See my gallery.

mac

The Mouser transformera seem to.havw a bit better output...i bought them really for impedance matching. Im going to be using the amp for studio use only really for tone as opposed to loudness

I know that RG's site had a nice tutorial on how to test gain and leakage on the transistors..

Is there a comprehensive reference on how to bias them as well? Perhaps for the transformers too?

[mac]

Mouser has better options, xicon IIRC.

You could try replacing one the base resistors of the driver transistor with a pot, say the one from vcc to base, and adjust for optimal sound.
And use a pot instead of the fixed 2k2 at the power stage to get the optimal current at the base of the power transistors. Beware of too much current, you could burn your Germs.

mac

[byod]

Mouser has better options, xicon IIRC.

You could try replacing one the base resistors of the driver transistor with a pot, say the one from vcc to base, and adjust for optimal sound.
And use a pot instead of the fixed 2k2 at the power stage to get the optimal current at the base of the power transistors. Beware of too much current, you could burn your Germs.

mac

hello Mac
could you please be more precise about the 2 resistors you are talking here ?

You could try replacing one the base resistors of the driver transistor with a pot, say the one from vcc to base, and adjust for optimal sound.

R6 ?

And use a pot instead of the fixed 2k2 at the power stage to get the optimal current at the base of the power transistors. Beware of too much current, you could burn your Germs.

R10 ?

the bias is supposed to be on R13

thanks for you help

[mac]

Yes, R6 (or R7), and R10.
Warning, if you lower R10 too much you could burn the power transistors.

I wouldn't change R13.

mac

[byod]

thanks for your prompt reply

my issue is that the note fade out in a strange way, like there was a noise gate

i read it was because of mis-bias so i'll try with 2 trimpots on R6 AND R10

any advice is welcomed

[mac]

Check Q1 too.

mac

[byod]

3 trimpots, i guess it will not be easy to tune haha

do you remember if you made the fryer (image below ) or the KAT version ( http://www.deacyamp.com/download/KAT_Projects/KAT%20Deacy-Style%20Amplifier%20Unit%20Project/KAT%20Project%201%20Watt%20Deacy-Style%20Amplifier%20Unit.pdf ) ?

[thermionix]

byod = build your own deacy?

[byod]

lol
never thought about that,
it s "bring your own device"

very bad nickname when you are not inspired

[mac]

do you remember if you made the fryer (image below ) or the KAT version (

Mullard schematic.
However I'm using a National radiorecorder which sounds louder and similar

Actually, the Deacy is a Supersonic PR80 and the output transformers seems to be an autotransformer. Some day I'll wind my own.

mac

[zbt]

sorry for wake up post, cause I want a bit more complete information

from fryer site
https://fryerguitars.com/deacy-amp/

project from github by jareklupinski
https://github.com/jareklupinski/deacy-amp

The Mullard and PR80 is different a specially at output, the transformer is different
the bias trim like slide pot, from other forum
https://groupdiy.com/threads/deacy-amp-transformers.78997/page-2

I trace pcb but dont know the size of it probably 10 x 6 cm



For silicon transistor would it be the same?
The speaker I found so far would it be work?
https://resources-boschsecurity-cdn.azureedge.net/public/documents/LHM0606_00_US_Data_sheet_enUS_1945383179.pdf

Also I wonder the transformer that make a good sound, cause tube amp are OT also?

[Clint Eastwood]

Hi,

That speaker, looking at the datasheet, has a high impedance, for use with a 70 volt line transformer. You need a 4 or 8 ohm speaker, depending on your output transformer. Get one with high efficiency if you can (that is the dB number in the specs).

Amplifiers with output transformers, tube or transistor, produce a special distorted sound when overdriven. Has to do mainly with the magnetic field through the transformer core collapsing at overload, and the limited frequency response.
Also, germanium transistors sound different from silicon in these applications.

[zbt]

Hi Mr. Clint, thank you for reply

Amplifiers with output transformers, tube or transistor, produce a special distorted sound when overdriven. Has to do mainly with the magnetic field through the transformer core collapsing at overload, and the limited frequency response.
Also, germanium transistors sound different from silicon in these applications.

Ok, so it make specific distortion too.

Without transformer the speaker impedance is 4 ohm (see circuit diagram) can be use for deacy.

Currently I have no idea for the amp that use the transformer other than tube which sound like tube 

[Clint Eastwood]

Ah yes, I did not see the speaker has its own line transformer.

[anotherjim]

4 ohm is a better match for the LT700 output transformer. I think 3 ohm is the "ideal" speaker for those but you won't find many of those new, they were once common in the days of class-A tube amplifiers. The Xicor (Mouser) ones are for 8 ohm speakers?

[zbt]

The transformer is included Sir,
it is mount to the speaker.

[anotherjim]

Those line transformers are often well suited for class-A tube (which you already know) although I'm sure someone has done it with class-A transistor drive.
If 3 of the transformer taps have equal winding turns between them, it may be possible to use with the Deacy class-B push-pull scheme. The diagram suggests that the 3-watt tap is between the 1.5 and 6-watt taps. So the 3-watt would be the centre tap connection to -9v in the Deacy and you don't use the 0 tap. You can confirm this by measuring the resistance between the taps. If we know these resistances someone might be able to estimate impedance and if it's suitable for the Deacy. Resistance too small might damage the transistors or too high give less power than it should.
I think the LT700 in the scheme has about 30 ohm DC resistance between the taps.

[mac]

A few days ago I opened an old Philips radio recorder with a TDAxxxx chip and connected the guitar to the mag head input @ pcb.
Set it to Tape and pressed Play ... No Brian May ...  but Norman Greenbaum   

mac