Constructors' Gallery – Page #4

Last Modified: 26 Aug 2016

A selection of constructors' valve amplifier projects photos that I have been given – some of them using transformers from Danbury Electronics, when we were still trading.

Click any image for full size and slideshow.



Tony Hamilton

Tony-Hamilton-1 Tony-Hamilton-2 Tony-Hamilton-3
Tony-Hamilton-4


Scott Frazer

Scott-Frazer-1


Dave Clarke

Dave-Clarke-1 Dave-Clarke-2 Dave-Clarke-3


Todd Ferguson

Todd-Ferguson-01CFE24F Todd-Ferguson-01CFE24F2


Peter Baxter
A few months ago I purchased two transformers and a 10H choke so as to construct a Williamson amplifier. I have scaled down my version physically and hopefully this makes it more suited to life in 2015!

IMG_1461 IMG_1462 IMG_1463 IMG_1464

The amplifier is constructed on a standard Hammond chassis from Farnell 12" X 8" X 2" and performs without fault. IMHO it easily exceeds the performance of the original and very large PX4 version I had back in 1970! The Danbury 1041V output transformer is ideal for this design and there is zero instability with this layout which is basically the same as that originally specified for the Mullard 5-20.

The 4 main coupling capacitors are Vishay 220n 1kv DC items from Farnell and are mounted underneath the main circuit board. All the components employed are straightforward high quality "everyday" items.

The valves are currently 2 X JAN Philips 5963 (ECC82) 2 X JJ KT88 and a Sovtek 5AR4 (GZ34).

I have disposed of the Williamson cathode bias arrangement and each KT88 has it's own 470 ohm 7W cathode resistor each bypassed with a 220mfcapacitor.

The bias arrangements to the first two valves has been changed slightly to better accommodate the use of ECC82/5963's. The plate voltage on each ECC82 driver is now 220V.

The amplifier is quite happy with either EL34's KT88's or KT66's as PA's.

NFB is adjustable using the pre set pot mounted underneath just adjacent to the main 220k input level control. The`1st af amp triode has a 1k cathode bias resistor in series with this NFB adj pot which is 100 ohms. NFB is applied to the wiper of this 100 ohm resistor. There is no capacitor employed as a cathode bypass component.

Much greater HT smoothing has been utilised to assist the noise floor and to aid the amplifiers handling of transients etc.

I am running an HT rail of 430V and I estimate the output power at circa 30 Watts into a pair of B&W DM602's. Input sensitivity is set at circa 500m/v.

Power is certainly more than adequate for our humble living room!

I have also constructed a Radford "clone" which at present I use as the other channel. It is of similar physical construction. I have, also, a "new" Mullard 5-20.

The original idea was to see which one I liked the best and then build two of the same! However, this strategy is the path to madness as they all sound pretty much identical.

I think it was the late Peter Walker who once said that all high quality amplifiers should sound the same :-).

Many thanks for your interesting web site and trust the enclosed is of some interest.




Pierre-François Cannet
Homemade AC15 head amp clone...

archaos-AC15-head-1 archaos-AC15-head-2 archaos-AC15-head-3 archaos-AC15-head-4



Fabio Bonucci
Hi Mike, attached is my last homebrew guitar amplifier. It uses a couple of type KT-66 valve (or 6L6GC). Transformers by Danbury Electronics, both mains and output.

    GA-50 standard Features:
  1. a Amplifier type: Push-Pull with negative feedback (Option 2: Ultralinear).
  2. Power tubes .. 2 X KT-66 "Kinkness Tetrode" (Option 1: 2 X 6L6GC Beam Tetrode).
  3. Class AB1.
  4. Power Output ... 50 WATTS R.M.S.
  5. Distortion .. less than 5% at max power output.
  6. Transformers by Danbury Electronics, UK.
  7. Preamplifier tubes ... 4 X 12AX7 (aka ECC83).
  8. CLEAN - LEAD - OVERDRIVE channel, selectable by front panel switch and/or custom footswitch.
  9. Built-in Lead channel (asymmetric clipping) by selected germanium clipping diodes.
  10. Built-in "True Tube Overdrive".
  11. Master Volume, Depth and Presence pots on final stage.
  12. Bass, Middle, Treble pots on preampli stage.
  13. Independent preamplifier gain pots for Clean/Lead and Overdrive channels.
  14. Selectable 4 / 8 /16 Ohm speaker output impedance.
  15. Cold blue internal light (LED).
  16. Handcrafted Point-to-Point (no PCBs), Mallory caps, Metal film resistors.
  17. Aluminum chassis - Lamellar 20mm wooden cabinet with carbon fiber finish (Red or Black).
  18. Dimensions (mm): 540 (W), 200 (D), 240 (H).
  19. Weight: 14 kgs.


Bonucci-12 Bonucci-4 Bonucci-9 Bonucci-10




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