I received an email from a guitar player in Sydney who had come across a little amp made by an Australian manufacturer sometime in the '60's. The amp was made by Diason and affectionately  called the "Baby". (There is also a model called the 'Bovine'. Please check out Australian valve amps for more info on both of these amps). Anyway, the owner had a fair bit of amp and electronics knowledge himself but was having a few problems getting this amp going right. One of the biggest problems was that the owner, Kevin, wanted the tremolo working ( as you would!). Unfortunately, the tremolo circuit had been removed, possibly in the hope the  triode it used could be used as an extra gain stage.

Kevin had searched extensively for a schematic for the amp but without any luck. (welcome to my world!). He did bring to my attention a circuit for a little 15 watt Marshall amp but this proved unsuitable. The Diason uses two 6GW8 triode/pentode tubes in the output stage and a 12AX7 in the preamp. I wanted a circuit that used these tubes and the Marshall didn't. I did, however, know of an amp that used the exact same tubes and was probably the same or at least very similar circuit. That was a Maton Mastersound 10. I have seen a couple of these amps come through the shop over the last few of years and fortunately one of them was owned by a good friend of mine from Huskisson NSW. I had the idea that if I could borrow the amp I could copy the circuit and repair Kevin's Baby. I finally wrestled the amp out of the hands of my friend and with a vague explanation that I just wanted to check out a few things on  the amp I got it back to the work shop where I promptly dismantled it. The Maton circuit is made on a printed circuit board which can be quite difficult to trace a circuit from but I persevered and eventually had a schematic from which I could build an amp from.

The Diason was actually working when Kevin mailed it to me but it sounded pretty bad and one output tube was getting a lot hotter than the other.  I did a few quick checks but didn't really figure out what was wrong.  I suspected maybe the output transformer was damaged but I decided I would face that issue later. It took me a while to getting around to doing this job and I thank Kevin for his patience but it wasn't the kind of project that I wanted to start and stop. I waited until I could put a whole day aside and had all the parts I needed and when that day arrived things went pretty smoothly. The first thing I did was strip out all the existing circuitry and control pots. Then, using my 80 watt soldering iron soldered in a number of tag strips next to the tube sockets and the mains transformer. Then, using a number of the original parts and a few new ones rebuilt the amp from scratch following the Maton circuit. The Maton uses the first triode in the 12AX7 as the one and only gain stage. the signal then goes through a passive tone stack into the second triode. The 6GW8 tube is a combined triode/pentode. The two pentodes are cathode biased and make up the output stage while one triode (in the 6GW8 case) is the driver and the other is configured to run the tremolo circuit. It is a compact little circuit and after powering it up and fixing a couple of small errors (this is where powering up an amp using a current limiter saves lots of explosions as one of those little errors was putting the rectifier diode in backwards!!) the new amp burst into glorious life. And wow, did it sound great. There was now obviously no problem with output transformer and I think there just must have been some wiring fault causing that earlier mentioned tube problem. I spent a little extra time on the amp tidying up a couple of things and it was ready to send back to the owner. I had it on display in my shop for a couple of days and I can't deny I was a little sorry to see it go. Fortunately, I was able to communicate with Kevin for a while as he emailed me a few questions and tried a few mods to tailor the amp's sound a little more to his taste so helped me to eventually survived my separation anxiety .

I have moved on now and am currently building a 5 watt single ended class A amp for a nice chap, called 'Nasty Old Dog' at the Hunter Harp Co-Operative in central Northern NSW. This will be the subject of another project page in the near future. When I get the time I am going to build another clone of the Maton amp for myself. It is a great sounding circuit that really captures that retro sound at a practical volume. And as Kevin said, the whole project was worth it just for the sound of the vibrato alone.

Here's the Baby before the rework.

Not bad for a 40 year old really.

Here is the amp's insides. The output transformer is on the left and the power transformers on the right. The input is on the left. You can see the 12AX7 socket base just next to the input and the 100K plate resistors and the cathode resistor and bypass cap. All the red sleeving is part of the previous owners rewiring job. All the  filter caps are original and were in good shape so I decided to reuse them. They can be easily replaced some time down the track if they fail or become leaky.

This is a close up of the Maton power supply. It has a full wave rectifier where the Diason had a half wave. I kept the original rectifier in the Diason and it worked fine. The blackness on the circuit board is from when the original X cap exploded a couple of years ago. I replaced it with the yellow one seen here.

When it came time to start the rewire I soldered a number of tag strips to the chassis and wired the components from them directly to the tube sockets. I used cloth covered hook up wire which is brilliant. You don't have to strip it before soldering but simply push back the cloth a little and put it in the spot you want and hit it  with the soldering iron.

Pictured above is the triode wired up an ready to rock and above right is the first of the 6GW8's. This tube contains the phase splitter and one half of the output stage. The wires coming up through the grommeted hole are from the output transformer. On the right is the new power supply. I decided to retain the original rectifier and filter caps. It's a bit crowded in there but I didn't have much choice.

This is the amp in the final stages of reconstruction. In the background is the Maton put back together. After I got stuck into this project ( and especially after I completed the copy of the Maton circuit , which was a petty big job in itself) I was very pleased at just how smoothly everything went. Using the cloth covered wire was a real time saver as was  having all the parts I needed already on hand.

That completes the Diason 'Baby' project and after doing this job I feel like just about anything is possible in  the world of tube amps. The beautiful thing about tubes is that they lend them selves so easily to these kind of projects. It would be very difficult to build a solid state amp on bunch of tag strips like I've done here. Like I mentioned earlier my next project, which I'm happy to say is coming along quite nicely is a single ended guitar amp based on a circuit from the AX84 project pages. After that I would like to spend a bit of money and build a Marshall JCM800 clone. These amps have a fairly basic circuit but man, do they sound great! Also, transformers for these amps are becoming reasonably priced and easy to obtain . I would like to thanks Kevin for his permission to use his amp in this project page and congratulate him on the great job he did finishing off this beautiful little Aussie amp. Here is part of an email Kevin sent me after completing the amp and putting it through it's paces.

. "The amp has become my main player at home, I love it . A good tube screamer type stomp box in front and you are away".

Regards Kevin.

(Please follow these links to another of Kevin's projects. A recreation of a Gibson les Paul Jr.)

Project Guitar 1

Project Guitar 2