Brian May 'Deacy' amp (tagboard)

[owlexifry]

a veroboard layout already exists for this circuit, but i wanna do a tagboard build instead.

deacy.png



schematic:
deacy.jpg


haven't built it yet, but i will when all the parts arrive :)

[fx-fidden]

I found this document:
https://docplayer.net/storage/40/21046937/1642951865/uXZJhEYF6Lx02--NrmVG5Q/21046937.pdf

Unfortunately, the schematic is not included, just the bill of materials that has some difference in the values with your schematic, especially in the resistors. Maybe because one of the two AC125 is an AC126?

In the document we can read something about the heat-sinks for the two AC128 that can get hot during the use.
Did you think about it?

[owlexifry]

couldn’t load your document..

yes. the ‘true’ deacy amp was based on a ‘PR80 supersonic’ radio, as outlined in this article:
https://hackaday.com/2017/05/08/a-queen-mystery-the-legend-of-the-deacy-amp/

this circuit had AC125, AC126, and 2x AC128.
this is seen in the schematic for the PR80:


what i have done is drafted a tagboard layout using the ‘greg fryer’ schematic, which i’m assuming was developed to ‘clone’/adapt the circuit from the PR80, using transformers that are actually available(?)
(this schematic substitutes x1 AC126 with another AC125, resulting in: 2x AC125, 2x AC128)

anyway, it’s the same schematic used for a veroboard layout that’s currently available, i found it here:

https://paulinthelab.blogspot.com/2012/06/brian-may-deacy-amplifier-stripboard.html?m=1

yes, i have ordered heatsinks for the 2x AC128 output transistors.

[fx-fidden]

Thanks for the info!

Could you link this kind of heat sink? I'm not sure I understand how it is.

[owlexifry]

no worries :)

here’s an example

https://www.ebay.com.au/itm/Transistor-Heatsinks-TO1-Heat-Sink-NOS-Vintage-5-pieces-/324684537775?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=710-127635-2958-0

https://www.ebay.com.au/itm/2-NTE410-Heat-Sink-for-TO1-Type-Package-Lot-of-2-/324326465007?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=711-127632-2357-0

[fx-fidden]

Thank you!

I don't know if I'm going to build it, too.
Do you think can I use it as a pedal? Replace the speaker with an output jack and go into an amp.

[owlexifry]

don't see why not, you'd need probably need to insert an output volume pot.... not sure if it would work that well or sound any good though....

[owlexifry]

this has now been built and verified.
works great!

only x1 update to the layout required (NFB gremlin)






updated layout:

[owlexifry]

evidence:

[fx-fidden]

Great!
Don't this amp have any volume control? Is it possible add any somewhere?
What did you use to add distortion in the demo?

Thanks.

[owlexifry]

there isn’t a volume control per the schematic i’ve been following.

no effects used in the demo.

guitar direct into the amp.

all tone variations come from the guitar controls.

demo starts on bridge humbucker at 2.5, dials up to about 5.5, then switches to cranked (about 8-9) neck pickup. that’s what’s causing the tone changes.

it’s a very different playing experience to what i normally do (high gain, metal etc.)

[fx-fidden]

So, a Pre-Gain pot could be cool.
I'm not sure how we could add a Master Volume control. Maybe in the end of the circuit it's not possible.

Thanks.

[induction]

Pre-gain and master volume should be easy to add. Master volumes don't go at the end of the circuit, they usually go between the preamp and the power amp sections. In this case, I'd try a 2u coupling cap into a MV pot (experiment with the value) right after the 2nd AC125.