PRR ThirdWatt Build Thread.

[FranciscoPerez]

Hello all,

I’ve been an every day reader of this forum lately, but not a great contributor I’m afraid…
Thought I could start a build thread about the construction of this amp, post some pictures of the building process, and maybe share some thoughts and experiences.

My goal is to build a low wattage amp as cheap as possible into a 1x10 combo somewhat smaller than a 5e3 cab. Never listened to this circuit, but seems like the perfect choice. Low power, transformers and tubes are very cheap, and most components I already had them lying around. I used a chassis I already had as well, made for a couple of octal tubes but otherwise perfect for this project.

I built the faceplate and board so far, and attached some components and tube sockets to the chassis. Really looking forward to finishing and plugging the amp!!

This is the thread I borrowed the circuit from:
http://el34world.com/Forum/index.php?topic=5039.0

And here some pictures:














I’m using 32uf-32uf-10uf in the power rail, do you guys think this is too much filtering? Have some of you built this circuit?
Thank you!! Especially to PRR for sharing this design.

[Paul1453]

Your faceplate looks fantastic!

The fix for the oversized holes is great, too.

Over-filtering does not seem to be a huge concern to me.

But PRR will obviously have the definitive answer to your questions.

Welcome, and post more often.   

[Ed_Chambley]

Looking good.  That is such a fun amp I actually have considered building it into a guitar.  Thanks for posting.

[PRR]

> too much filtering?

Spending money like a drunken sailor!

If you build a bridge or a house, you never use a 32-inch wide stick where an 8-inch stick will stand-up long enough to spend the money saved.

Not just cap-budget. Your board and case are bigger than they NEED to be.

The 1000V cap is also throwing profit out the window. 200V would be ample and cheaper. (But probably not "British Made"!)

Yes, yes, DIY is not about profit; and in this case you may need a build heavier than a guitar-cord so it doesn't slide around. I don't think the over-filtering does any sonic harm.

[HotBluePlates]

Nothing to do with the amp, bt I really like the 22 Nanofarads logo!!

[mresistor]

Nothing to do with the amp, bt I really like the 22 Nanofarads logo!!

Absolutely, that is a cool logo and faceplate.

[Willabe]

The whole thing looks GREAT!!!!!   

Where did you get those 7 pin socks? Are they Russian?

Do the pin cups hold the tube nice and tight?

[FranciscoPerez]

Wow thank you guys!!

Glad you like how the amp is turning out! I don't run an amp business or anything, and I keep most of the stuff I build for myself, but always thought it'd be nice to have a logo and a name to give my builds a more professional look :)

The faceplate is back engraved using Nd-Yag laser, and it works great!! The following image shows the same machine used to engrave one of my pedals:



The tube sockets are British made, bought from ebay. Since I'm in Spain, I bid a lot from British ebay users. This time they were bought from a guy whose ebay username is yitry. They are tightly fixed using lock nuts:



I'll probably use some heatshrink tubing on the socket pins, as the nuts are a little bit close to some of the tube pins.
Totally agree with you PRR!!! I should have used a smaller chassis and lower rated components, but I have more of those chassis, and those Plessey british capacitors, than I'd probably ever spend. Wanted to make use of them, to avoid ordering new parts.

Hopefully I'd bolt the transformers today and start wiring the whole thing. I'll keep up posting pictures of the process.
Thank you!!!
Fran

[JB]

Looking good!

I built one when PRR first put the schematic up.  We had a couple of threads running about low watt amps and he came up with this wonderful creation.  Sounds great, still loud enough to annoy other occupants in the house though - if running through a typically high efficiency 12" guitar speaker.  So that's why PRR added the variable screen control to reduce the output power.

You won't be using it for a clean sound - If you turn the volume (not the screen control) down to clean it up your strings will be making more sound than the speaker! 

[FranciscoPerez]

This is great news JB, for I wasn't after a clean amp this time!!  I'll be probably using a 1x10 or 1x8 combo cab, still have to decide which speaker to use. Suggestions?

[Willabe]

The tube sockets are British made, bought from ebay. Since I'm in Spain, I bid a lot from British ebay users. This time they were bought from a guy whose ebay username is yitry.

Thanks Fran.   

[FranciscoPerez]

Some more pictures with the transformers mounted, hole drilled on faceplate for the cathode bypass cap switch, and board in chassis.
Tomorrow's wiring day!! 

[FranciscoPerez]

Did some progress to the amp, hope you like it!
Looking kinda messy a the moment. I still need to solder the board to the tube sockets etc, wire the power supply ...
Anyway, here it is! Bought some tubes for the amp as well. They're so cheap I got two Phillips 6au6 and two Valvo EF94, just to try both and decide what I like best.


Cheers,
Fran

[FranciscoPerez]

Almost there!! Only a pilot light away to powering up the amp, can't wait to hear how it sounds!!!


Cheers,
Fran

[FranciscoPerez]

Hi all!
Had some free time to first power up the amp. After solving a couple silly mistakes    including a 470K resistor in the power rail instead of the needed 470R, I could take some measurements and eventually plug a guitar and play!!


My meter reads 172v - 165v - 135v  in the power rail. Preamp tube cathode reads 1.09v, and power tube cathode 1,16v.
No smoke, no fire, so everything looks fine. The amp is dead quiet at idle.


I had the chance to play the amp for a couple minutes connected to a 12inch alnico speaker inside a 2x12 cab and didn't sound bad at all! Really promising, can't wait to play the amp again!!


To JB, PRR, and others who built the amp,  what speaker/cab did you use with this circuit?? What do you recommend? I'll be starting with the cab shortly, and I'm thinking about a cab bigger than a champ and smaller than a 5e3, with a 8 or 10 inch speaker.


Thank you!
Fran

[HotBluePlates]

... To JB, PRR, and others who built the amp,  what speaker/cab did you use with this circuit?? What do you recommend? I'll be starting with the cab shortly, and I'm thinking about a cab bigger than a champ and smaller than a 5e3, with a 8 or 10 inch speaker. ...

Congrats!! 

I haven't built one yet, but will soon after seeing this. In all likelihood, I'll be using a 2x12 cabinet with alnico Celestion-style speakers.

[PRR]

I did not build this. It was originally a joke.

I see two ways to go:

Baby-nap: 4-inch old radio speaker. If you don't push it, it won't be too very loud at the far end of the house.

Baby-waker: Two 12-inch in a good open-back cabinet (a Twin); or even a Full Stack (8 Tens). None of your neighbors will believe it is well under a Watt.

[FranciscoPerez]

Thank you guys!!
No kids yet, so I'd probably go somewhere closer to the baby-waker :)

[JB]

Hi,

I ran mine into an open back 1 x 12" cab loaded with an EVM 12L!  1/3W amp into a 400W speaker, bit like a pimple on an elephant.

I told PRR it was still loud - which it would be with that driver - which is why he suggested the variable screen control to make it even lower powered! 

Sounded ok, was fun to fiddle with, then I moved on to big amps - 1W single ended and a 4W push pull both using EL91 miniature power pentodes!

I did also try it in a homebrew 1 x 8" combo cab, using a Celestion Super 8, but that was very boxy sounding with understandably limited low end.

[FranciscoPerez]

Thanks for sharing your experience JB!
I played the amp again today, and had enough time to give it a good whirl. Given its price and complexity, I honestly think it's quite awesome!! I can get clean-ish tones at moderate volumes easily with my tele, and the overdrive is surprisingly good. Turn the screen control down too much and it starts sounding harsh, but it's quite useful anyway, and really serves a purpose for me.
This thing is loud indeed! Perfect volume range as a practice amp for home use.
The weber alnico 12A150 speaker I'm running the amp with seems like a good match as well.


Can't thank PRR enough for sharing this design! It was a long shot, for I didn't have any idea about how an amp like this would sound, but I'm really happy with the result.
I'll post some pictures of the completed amp with cab when finished!


Cheers,
Fran