Bad case of GAS

[paggerman]

Hi all - you've all given me a nasty case of GAS. I'm loving your posts and it's going to cause trouble. It all started at Christmas when my son receieved a Yamaha Pacifica and VOX Pathfinder 10 from satan. Of course, he needs someone to learn with and soon after I bought an Abilene strat copy from ebay, accompanied by a 'Drive' 10W SS practice amp. the Drive amp will likely never be plugged in again in its current state. It sounds disgusting.

So I tried using an old hi-fi amp (Yamaha A500, c1984) and speakers with a cable I made with a cap and resistor to filter (I got the idea off the web somewhere). Parts AU$8. it didn't sound good 'cos it's too clean. The amp is great for hi-fi still.

Then I made a BYOC Mouse. It worked first time. Parts US$110. So I thought I'd try to solve my amp problem by building a Noisy Cricket. It worked first time, playing through an old hi-fi speaker. It sounds OK, but the finish is a bit shabby and it breaks up too easily. Parts AU$30 or so. By now, I was reading forums (fora?) long into the night.

I needed a reasonable amp and I really enjoy making stuff, so I thought I'd give making a valve amp a go. So I investigated some of the kits (ampmaker.com ceriatone ax84 etc.) and the costs of the kit was OK, but the postage to Australia is frightening (all that heavy iron, I suppose). Then I cam across the 'Lamington', a 15W PP amp designed for Australian conditions. Australian conditions meaning the iron's impossible to get hold of locally and it's hideously expensive to import. it's called a Lamington because the chassis is a cake tin for a particularly Australian cake called the Lamington. This tin doesn't look particularly attractive, so I substituted a stainless steel roasting pan from IKEA. several drill bits later and I have a drilled chassis, a bag full of components and valves on order from New Old Sounds. estimated cost (I won't say because this will be on the internet for ever and my wife could encounter it).

A week past Sunday I was walking the dog and passed a garage sale. I saw some old looking (are there any other types?) record players. I couldn't stop because the sale was busy and the dog is just a puppy and wouldn't have behaved. I've tried going back a couple fo times, but no-one is ever home. Tonight, success. I have bought a 'Nippergram' radiogram. It cost about the same as two packets of cigarettes.

I got home and took the top panel off. If nothing else, I have picked up a cabinet, small speaker and a chassis (Champ project?). From what I have learnt on these (and other pages) I should expect the caps to be toast (or to rapidly become dangerous if I ever switch it on), the two wire mains lead to be dangerous (even without the taped up join where the plug has been replaced) and the valves may or not be operative.

What about the iron? It looks like it's made of loosely wrapped wax paper! Is it likely to be unsafe? I've attached a bunch of pictures showing some of the key parts. I'd really appreciate comments about what I could potentially do with the this (other than aforementioned Champ project). What are the two big cans in the middle of the chassis (1st IF and 2nd IF)?

Valves: 6BE6, 6BA6, 6X4, 6AV6, 6M5.

So I now have two projects on the go - which is fun. And one day, I may be able to play more than three chords. My son's christmas present is getting a daily outing and one day I'll let him plug into the Lamington.

And yes, I am well aware that 300+VDC can kill me and that I should keep my left hand in the pocket. You guys certainly drill that one in very well and it's appreciated.

[axpro]

YIKES!!!!

I would be blueprinting what you have, and what youplan to do with it before you ever think of plugging it in.

I am not familiar with the valves (phono/radios used lots of wierd and wonderfula nd hard to find valves) but depending on the specs, you could rewire it to use some more readily available tubes,
For the price of a couple packs of smokes, it should be fun!

[RWood]

You could build something similar to what dynaco built in this thread:
http://music-electronics-forum.com/t18088/

In your amp you would use 6AT6 preamp tubes instead of 12AT6 because you have a 6.3 volt filament supply. They'll cost you another pack of smokes. There are other tubes that can sub there, like 6C4. You just need a triode in those positions.

Then you'll use the existing rectifier, 6X4, and power tube, 6M5.

Where dynaco's amp uses a series-stringed heater array, yours would be parallel daisy chain, and in fact you can leave all your existing filament wiring in place (pins 3 and 4 of your small, 7-pin tubes).

Also leave in place your transformer-to-6X4 wiring (replacing the filter caps that follow the 6X4's DC output) AND all the wiring to the 6M5 (9 pin) power tube save the input, pin 2

You'd gut the rest and rebuild per his schematic with the two different preamp tubes, ending up with a new connection to the control grid of the 6M5 (pin 2).

It has potential for a cheap but very educational project as it has all the elements of a bigger guitar amp, but on a smaller scale. No, it'll never produce gig-able volumes but it will be a fun and rewarding project.

RWood

[Steve Conner]

Don't worry about the "wax paper" appearance of the transformers (though that's exactly what it is, wax paper!)

I've seen plenty worse that worked fine, the only reason to be worried is if you see evidence that the wax has melted and dribbled out. That indicates the transformer was overheated at some point in the past, probably due to a faulty component somewhere else.

[paggerman]

More Gear Acquired

At my local dealer yesterday (getting resistors to feed the habit) and I was walking down the laneway from the car park and I spotted an electric organ next to a skip (dumpster) outside a charity shop. Enquired inside - they can't sell electrical equipment (safety), so it just gets landfilled. I asked if I could take some bits - help yourself, make a donation. took a 12" Kawai speaker (one small hole), PSU (big iron, probably step down) but it was shielded by an aluminium box (future chassis), 6 knobs, reverb tank (at least that's what I think it is - two 6" sloppy springs, small coil and RCA at each end) and 2-jack panel. When it came to payment they refused anything more than AU$1. Not even enough for half a cup of coffee!

[petemoore]

Ground the Chassis to Earth, use an IEC or strain relieve a 3 pronged cord/plug.
...assuming that big iron is an AC isolation/voltage transformer.

[paggerman]

You could build something similar to what dynaco built in this thread:
http://music-electronics-forum.com/t18088/

In your amp you would use 6AT6 preamp tubes instead of 12AT6 because you have a 6.3 volt filament supply. They'll cost you another pack of smokes. There are other tubes that can sub there, like 6C4. You just need a triode in those positions.

Then you'll use the existing rectifier, 6X4, and power tube, 6M5.

Where dynaco's amp uses a series-stringed heater array, yours would be parallel daisy chain, and in fact you can leave all your existing filament wiring in place (pins 3 and 4 of your small, 7-pin tubes).

Also leave in place your transformer-to-6X4 wiring (replacing the filter caps that follow the 6X4's DC output) AND all the wiring to the 6M5 (9 pin) power tube save the input, pin 2

You'd gut the rest and rebuild per his schematic with the two different preamp tubes, ending up with a new connection to the control grid of the 6M5 (pin 2).

It has potential for a cheap but very educational project as it has all the elements of a bigger guitar amp, but on a smaller scale. No, it'll never produce gig-able volumes but it will be a fun and rewarding project.

RWood

Thank you so much for this advice - I commented on Dynaco's design before you replied to my question - so I feel utterly obliged to make this now. I'll let you know how i get on. Very many thanks.

[paggerman]

Hi Steve, there is goop on the PT, but it all seems to work fine (tested 300v-0-300v, 210v, and nearly 7v on secondaries with nothing connected). Is this likely to be a problem if I continue to build? Many thanks.

[Steve Conner]

Well, some of them are just goopy like that. They get dipped in hot wax at the factory.

It's only a cause for concern if the wax re-melted at some stage in the transformer's life and dripped out all over the chassis. That's a tell-tale that it was overheated.

Even if this was due to a fault somewhere else in the equipment, when a transformer has been badly overheated once, it could fail later. Or it might be fine: wax melts easily.

I'd leave the PT running with no load for a few hours, verify that it doesn't overheat, smell bad, smoke, or make ominous sizzling or frying noises. (Keep an eye on it.)

[raiken]

It all started at Christmas when my son receieved a Yamaha Pacifica and VOX Pathfinder 10 from satan.

I think you have bigger things to worry about if satan is giving your son Christmas presents...

[paggerman]

A new amp is born.

Well, a new amp is born. Weighing in at over 2Kg (maximum reading of the kitchen scales) amp and builder are doing fine. Over the weekend Little Ripper was really quiet even though all vital signs checked out as being OK. Little Ripper was put away to incubate for a while. This evening I started testing again and all vital signs were still OK, so I fed some sweet harmonics in and heard the sound of amplified guitar. Nice low volume clean, cranking up to reasonably strong overdrive. I haven't really provoked Littel Ripper yet as there is a sensitive environment and i don't want to disturb other family members. A little background hiss which is OK, but i do get an earthing problem hum that disappears when i touch the strings or the still naked volume pot shaft. I'm really proud of this build as I have used my learnings from these pages and Merlin's website to apply principles that have worked a treat. Furthermore, all of the expensive bits - PT, OPT, power tube (6M5) chassis and even the speaker I have picked up for next to nothing. My investment has been in electro filter caps (two sets, oops!) valves (2* 6AT6) and a handful of cheap resistors and greencaps. Time is another investment but that has been worth it. I have also picked up a few other bits and bobs along the way (soldering iron and DMM) that will be used for years to come. This has been a great education and lots of fun - just like RWood said. The finished product ain't pretty and I'm definitley not a carpenter so it may remain naked for a while. I'll just enjoy my handywork! Circuit diagram attached. Cheers.

[RWood]

Congrats to the proud parent and NICE schematic. You might not be a carpenter but you could be a draftsman. Or draughtsman. Whichever is more convenient.

Glad to hear your amp works. Re the grounding - could that be the guitar? Do you get that same amount of buzz when you plug it into a different amp?

Let us know how it sounds fully cranked!

[paggerman]

Little Ripper follow up

Congrats to the proud parent and NICE schematic. You might not be a carpenter but you could be a draftsman. Or draughtsman. Whichever is more convenient.

Glad to hear your amp works. Re the grounding - could that be the guitar? Do you get that same amount of buzz when you plug it into a different amp?

Let us know how it sounds fully cranked!

Thank you for your praise re the diagram. I use Visio for work on a regular basis and using it to create a schematic was a 'transferable skill'.

On further investigation it sEems the guitar is a considerable source of hum and buzz. It is a HSS strat-a-like. If I turn down the tone to zero, most of the buzz is eliminated. If I put the switch in the second position, most of the buzz is eliminated. The level of buzz drops considerably if volume is set to 10 on the guitar (it's a sudden change when on the limit). This goes with all 3 of my amp builds to date. It's not as bad into a Vox Pathfinder 10 (SS), but still there.

Any tips on reducing the noise from the guitar, or is it time to start planning the conversation on why I *need* a new guitar?

Thanks all!