New build - 18 watts of salvage! - GuitarTalk Community

New build - 18 watts of salvage!

TomOlsen1

Hey guys

I recently bought an old DIY valve hifi off Michon (also a member here). 2x EL84 (Siemens) , 2x 12AX7 (Telefunken and siemens) and 1x EZ81 (Telefunken). And..... an original RS OT in unknown condition. Michon couldn't get it to produce sound through a speaker, but said that the OT was making noise when connected without a load. I bought the amp voets toets, with anxious testing sessions over the next few days...

TomOlsen1

First up, testing the tubes. I tried the tubes in my Marwatt, and wouldn't you know, they're all bloody gorgeous. Next up, OT. I grabbed a wiring diagram off the web, a few quick tests with a DMM and so far so good. So I connected it to my amp, and it's working!

Last up, power transformer. Interesting piece, has a bracket with a voltage selector and a mount for the rectifier tube bolted on. No center tap for the heaters, and rectifier and audio tubes on the same heater supply. That introduces hum, so the final build will have to diode rectified.

Voltages are a bit low at first, but then figured out the voltage selector is on 245v primary rather than 220v primary. That sorted, getting a solid 6.7v on the heaters and should get around 370v B+ rectified. That will be bloody perfect.

Now that everything is in working order, it's time to strip the chassis and plan my layout. Many of already drilled holes aren't straight or equidistant. It's messing with my OCD.

TomOlsen1

The more I think about it, this amp would be perfect for an 18 watt lite IIb. Maybe even with power scaling. In fact I have a faceplate laying about.... does it fit?

That's a yes! Have to drill some new holes for it and trim the plate, but that should do nicely! Quick, to the photocopier Batman!

Have I mentioned how much I hate drilling steel?

And after some careful work with a junior hacksaw

TomOlsen1

Okay, time to mount the PT and OT. I've decided to keep the RS OT for another build, so going to use a locally wound RS clone from P Souris.

PT orientation is 90 degrees off, so need to change that. So after much swearing and VERY careful drilling, all holes are done. Some primer and some black hammertone and we get this

Starting to look like something....

TomOlsen1

So, there are a few considerations to make regarding the circuit and layout

1. No centre tap for heaters - going to make an artificial one with 2x 100 ohm resistors. Also going to attach this to the cathodes for the EL84s to elevate this to DC to reduce hum even further.
2. SS rectification - not going to bother with a sag resistor.
3. Parts - as luck would have it, I have enough mullard mustard caps to do an 18!!! Substituting a 6n8 for the 4n7 on the one control, but close enough.
4. Space and tube placement - hmmmm. The L shaped placement of the tubes presents a problem. I can't fit a turret board in there. Going for 4x terminal strips. One pair by the 3 tubes in the vertical, set up as phase inverter and the two output tubes. Will have a single terminal strip by valve one, and another for the VVR and first filter cap. Proposed layout as below:

TomOlsen1

Wiring it up

OT, input and output jacks and pots

Heaters, PT and starting placing components

Output tubes

Phase inverter

All done!

TomOlsen1

Lastly, some graphics with some help from my wife

TomOlsen1

How does it sound?

Well, like this:

ezietsman

urgh, that sounds great. Good Jarb! ?

guitarboy2828

This post just gives me butterflies! ? ? I love it! Thanks for sharing. My dad has 3-4 of these old tube amps.

I just bought a 18w kit from Karel Mars. After I've finished that, may have to tackle some of the old tube amps and do something like this!

TomOlsen1

Thanks guys!

@Ez - next up, an EZ68! Best. amp. design. evar. EVAR!

@Paul - the bug bites pretty hard after the first build. The cathode bias low wattage ones are the gateway drug. But, there's no substitute for big bottles and big iron. Hence my sentiments above. Seriously, Ewald's amp is the best thing I've ever played. Just waiting on a few parts to arrive and quotes on the iron. Then it's on! But enjoy your build, and be careful.

Micron

Nice build. I'm glad I sold it to someone that put it to such good use. It sounds great too.

Now why don't you buy the remaining Philips amps I have? (Think of all the Philips and Telefunken tubes hidden in those enclosures) ?

Norman86

fark me. sounds great! looks great! Nice one!

wern101

That tone is absolute magic! Wow wow wow. So jealous!!

shaunf

Freaken awesome!

TomOlsen1

Thanks guys!

Doing a little more work on it this weekend, just adding rubber feet, a handle and a strain relief for the cable. (Or if I'm feeling VERY motivated, maybe a kettle cord in) And cleaning up the power transformer, heat shrinking the remaining exposed terminals.

The hammerite isn't as hard wearing as I'd like. If I was doing it all over again I'd pay to have it powder coated.

singemonkey

Your 18W sounds better than ours. Asshole ?

rikus

That looks and sounds super sweet!

Are those valve sockets mounted on the the transformer?

TomOlsen1

@Alan - nah, it's just a flattering recording. Same circuit, same voltages, same OT. You can't go wrong with a Lite IIb.

@ Rickus - the valve socket on the PT was for the EZ81 tube rectifier it used to have. But it was on the same heater circuit as the audio tubes, which can cause hum. I decided to go diode rectified instead. That weird bracket also has the voltage selector, so decided to leave it on. But I put some heat shrink on there to insulate over the weekend.

petercornell

Congrats!

Nice build, awesome tone.....