BAJA Powertwin 100 photo essay

Tube or solid-state, this section goes to eleven!
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bajaman
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Post by bajaman »

Hi folks
This is what I am currently working on - a modified dumble inspired guitar amplifier with a stereo return loop and two 50 watt output stages.
I purchased the chassis from Nik at ceriatone.com (overtone special), and drilled a few extra holes to accomodate the extra driver tube and output transformer. as you can see from these first pictures, I am using cream coloured front and back panels. The finished head cabinet will be covered in British Racing Green vinyl. The large internal component and filter capacitor boards (not in pictures yet - except the rectifier, relay power supply and fet amp stage boards)are hand made with 1/8 rivets and 2mm fibreglass. Notice the dual ganged master, resonance and presence potentiometers.
As you can see, I have a lot of wiring to do yet before this baby sings.
More soon - I better get back to the mountain of repairs waiting patiently for me.
Cheers
bajaman

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salocin
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Post by salocin »

nice.

you planning on selling these or is it just a one off for yourself?

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bajaman
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Post by bajaman »

Hi salocin
you planning on selling these or is it just a one off for yourself?
It will be for sale - i will probably auction it on Trade Me NZ - it will NOT be cheap though - hand building with top quality components cannot be compared to mass produced "product"
I will let you know the price once it is finished and before I list it. :wink:
cheers
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Post by rocklander »

'tis a thing of beauty alright... will it come with earplugs, or an indemnification clause for loss of hearing :wink: :applause:
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Post by Fuzzer »

Wooooow, that's badass. Congratulations.
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Post by soulsonic »

Fancy!
Are those Belton sockets? I love those. :D
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Post by bajaman »

Are those Belton sockets?
yes
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Post by chromaticdeth87 »

nice. HRM or skyliner type? Maybe my eyes are playing tricks on me but it looks like you have to two power trannies or outputs? I see four there. Is one the switching tranny? Nik makes awesome stuff. What brand xformers are you using?

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Post by soulsonic »

The smallest transformer is a filter choke for the power supply.
There are two output transformers because it's stereo! :D
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Post by RnFR »

FET input? don't tell me- 2SK1117 right?
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Post by bajaman »

FET input? don't tell me- 2SK1117 right?
No - not this time (2SK117) :lol:
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Post by chromaticdeth87 »

gotcha. stereo, makes sense in a way.

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Post by Nikifena »

Looks great BAJA!!!
:applause:

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Post by bajaman »

Thanks for the nice comments :D
I have just uploaded a few more pictures, showing the power supply and wiring of output tubes, speaker sockets input to fet preamp and the front panel earth bus etc.
Time for a nice cup of tea now - more in the next few days - these things take time and a lot of patience.
enjoy
:wink: bajaman
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Post by bajaman »

some notes: the power tube heater wiring may look a little unusual because it uses a 12.6v ac winding on the transformer - therefore each output socket pair are connected in series and then both channels are paralleled - hope that makes sense :hmmm:
The transformer originally belonged to a Holden 100 combo running a pair of KT88 tubes - the ht winding was 500v ac!!!!
I managed to find a point on the winding that gives me a much more respectable 350v ac unloaded - perfect for this project! Hope that makes sense too!!
more later - me tea's going cold :(
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Post by Nikifena »

^ hm..
I never try this heating wiring.

Try it! Don't forget to solder two 100 ohm/2W resistors from heating pins to GND to reduce noise.

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Post by jrc4558 »

Awesome! How heavy is it, with all that iron? :applause: :horsey:

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Post by bajaman »

Awesome! How heavy is it, with all that iron?
and copper !!!
....only about the same weight as a jcm800 100 watt head (aluminium chassis not steel)
cheers
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Post by bajaman »

More pictures just uploaded:
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12 - v1 and v2 terminal boards plus footswitch socket and send return socket wiring
13 - front panel switches capacitors and resistors - get on the bus :wink:
14 - bajalator board exposed and developed - ready to etch
15 - halfway through etching in pyrex jug over gas stove - using ammonium persulphate crystals
16 - 10 minutes later - all etched
17 - etched and scrubbed with scouring pad - shhh, don't tell the boss
18 - the stuffed board - okay, I had to drill the holes first - notice the large mosfet (the wrong way around :slap: ) and the two 4.7uf electrolytics - I removed these as they were not needed. The voltage gain is approximately 30 times without them, using J201 n jfets from +40v dc supply rail.
19 - another completed incorrect board
20 - the other side - ssssooorrryyy aboouuut thhheee shhhakesss
21 - the correct board layout - mosfet the right way around and no electrolytics fitted
22 - shaking again - this shot shows the missing 1M8 resistor between the drain and gate of the mosfet needed for biasing purposes
23 - aha!!, the main preamp and driver board fitted with the bajalator board mounted above send and return sockets at rear
24 - another angle
25 - up close and riveting :lol:

more again soon
enjoy
bajaman
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Post by seniorLoco »

Nik is cool ....he has been a good support and just 3 hours away .... 8)

Bajaman ...very nice ...this time i can't wait for sound clips :mrgreen:
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