36 watter gigging, 54W ? 72 W ? 'watt' next

[stevesuk]

Now the 36 watter is happily gigging I thought what next ?

I have been tidying up my pile of amps and uncovered my Sound City 120 watt which has 6 X EL34s, I got to thinking. 6 X EL84s ? 8 X EL84s ?

As the 36 Watter retains the character of the 18 Watter but louder, I wonder if this would hold for 54 Watts and 72 Watts.

It will fit in a 'normal chassis' as the Sound City is not huge. I have a large Partridge PT that would do the job. The OT is another consideration. Looking at the SC 120 diagram the 6 valves are just push-pulled in two pairs of three, assuming this would hold good for any even number of valves. The Impedance of the OT would just be calculated using ohms law, just as the 36 watter. e.g. 2 X EL84s = 8K, 4 X EL84s = 4K, 6 X EL84s = 2.66K and so on..
To illustrate just how much can be packed onto a chassis, have a look at the SC120 watt pics attached. Now where is that drawing board ?

Steve UK

[Ballz]

Well, while it gets a little bit louder, it also carries consequences. You will eventually need speakers that can cope with it. Your 8 x EL84 suddenly MUST have a 4x12" of 200-250-300W capability in order for the speakers to survive the square waves.
Also, your PT and OT will need to be substantially larger. Personally, I think the extra loudness is not worth the effort. After all, you need to become ten times more powerful to be twice as loud....so IIRC:

if 36W is loud enuff for most venues already (which I claim it is!) ...You will need 360W to be twice as loud. I´d rather put those 360W into 20 smaller jaw-dropping (" - What was THAT?") amps



/Richard

[Plexi]

Steve; yep you get the idea. The Sound City looks in great shape.
Most might cringe of the thought of you tearing it apart to build an amp from it. But for those who may have an old amp,they do make adapter sockets,if someone wanted had an amp with octals.
I myself think alot of the sound comes from the 84s..
but you could use a different tube,like the EL34s And much easier to find the trannys to do that job. The SCity you could use the octals and use EL34s And maybe just use 4,for a pretty loud amp,Use the E34L[30 watt tubes]. You could change the OT or do the switch change for the impedence.. So most of your parts are there.
There are alot of people that like those Sound City amps, might be easier to sell it,and just buy parts or trade for an amp you think would suit you better. I use to own one of those,picked it up for 50.00 Looked like new,but didn't work,so i got it cheap. All that was wrong with it was a power cord..lol I like the 50 plus much better,that can be a great sounding amp.

Richie

[stevesuk]

Richie,
I didn't intend to strip the Sound City 120 Watt, although it needs time and well known modifications, as it has the famous 'light aircraft buzz', Sound Cities are famous for, despite replacing all the Can Caps which took hours. It is an ideal C & W type amp as is stays clean until your ears give up. Just that I loath C & W. LOL.
It makes a suitable heavy PA thats about all it's good for. But, like you said, this one was a cheap non-worker with a few broken connections and burnt out valves, easily fixed.

I have made up 6 X 18 watt size chassis blanks, and have a spare large Partridge tranny. So, rather than get bored just churning out 18 watters, I thought i would experiment a bit. After all, the components, valves, board etc. are cheap enough and a few more valves, bases and resistors etc. would be all that's needed. I might just make a few 36 / 18 watt switchables. Kevin O'Connors Ultimate Tone book has some interesting switching techniques.

I am looking forward to including on board reverb when we get the circuit on the site.
Steve UK

[loverocker]

Steve

Here's an idea if you want the 18W tone louder... and more flexible... and with reverb in the proper place (post distortion):
* build a Lite II in the chassis
* build a dummy load for the output (no speaker)
* take a feed from the dummy load for reverb input
* take wet reverb return and mix (in parallel) with a dry feed from the dummy load
* feed the result into the SC's clean power stage, via TMB+P EQ

This isn't new of course - it's *exactly* the approach of the Guytron GT100 to which I'm a 110% convert. I think there's some patented cleverness around Guy's dummy load arrangement for the EL84's. But you do get THAT tone at anything from milliwatts to 100W+

[Graydon]

LR,

I did a similar thing once at home. I ran my 18W into a MASS attenuator turned all the way down. I ran the lineout from the MASS to my power amp return of my Dumble-clone (100W power amp) and ran that through a speaker. It sounded very good and I could get the sound of a barely broken up 18W at any volume I wanted. Also, I could get the sound of a severely overdriven 18W at any volume I wanted. You're right too, that is the general approach of the Guytron. Guy does have some fancy things going on in the 18W attenuator. It isn't a simple OT like we use on our 18W.

[jaysg]

I might just make a few 36 / 18 watt switchables. Kevin O'Connors Ultimate Tone book has some interesting switching techniques.

Since I'm lazy...don't have the time...er...well anyway, if I had the time, I'd try that with on-the-fly-fet switching and different PIs for each pair. I wonder how the full jersey-arron PI on one pair, and the stock circuit on the other pair would go. I'd want to be able to A/B/A+B it from a footswitch.

[stevesuk]

It seems we have only just started on this 18 Watt thing and the only limit is imagination, inspiration and motivation. Particularly when you ' roll your own ' and I do mean chassis'

I have been talking to a builder today about converting the garage into a purpose built amp building room. I think I may have ' The Buuug'.

I am now transferring my discussion to the BBQ to solicit opinions on what to put in a purpose built amp building room.

Steve UK

[jaysg]

I am now transferring my discussion to the BBQ to solicit opinions on what to put in a purpose built amp building room.

That's easy. Start with a refrigerator.