low wattage all tube

[phil]

Phil you say I can use the same PT & OT from the VJnr in the HeavyWatter??  I wasnt aware of that.  I am very interested in being able to make a heavywatter on the cheap and then as you say there is the possibility of making a firefly also..

On reusing the PT and OT transformers for the HeavyWatter:

On 18Watt.com there was a post from someone that asked what they could do with the OT from their modded VJR and one of the answers was to use it for the HeavyWatter - the Fender Reverb OT (which is specified in the Heavywatter schem) has a secondary impedance of 8 and the stock VJR has an impedance of 7.5 which is close enough (interesting since the EL84 in the VJR really works better with 5ohms). It also has 8ohm and 4ohm speaker taps.

As far as the PT - it has taps for 6.3v heaters AND 240V. Because the VJR PT is not center tapped, there's a simple change to the design to be able to use the VJR PT ... instead of using 2 diodes, you'll need to use all 4 diodes in the VJR in order to make it full wave rectified.

Since the Firefly is PushPull and not Single Ended, the VJR OT can't be used. So we'd need to buy something like a Hammond 125C.
But the VJR PT was confirmed as being usable for the Firefly in one of my posts in ax84.com, so that would still be usable. Pretty much the same
change with the rectification as above, but additionally, just need to add a 5 watt dropping resistor to lower the b+ voltage about 85v.

I think if its something you are serious about we should combine forces on it a little would seen silly for two of us to be working on the same project and not sharing brain power

Sounds good to me  - I'm more than happy to share whatever I find out, but you should know that I'm pretty new to amp building, so take what I say with that in mind - I've modded a couple Valve Juniors, and I've build a Marshall 18 lite from a kit, but I've never built anything from scratch. I suspect that you probably have more experience than I do at this point ...

I'm wondering if we should create a new thread in the General Discussion area of ax84.com since this is more about Tube Amp building than effects building? I think we may be going off topic in this area, but also, if we are posting in AX84, other more experienced builders may be able to weigh in on our discussions as well ...

[Papa_lazerous]

Yeah it is getting just a touch off topic in here.....

I am not experienced in valves at all.  I am mid build on a matchelss hotbox preamp its on hold till I move house though,  a small valve amp is my main concern though as I just cant play with what I have where I am going.

The building of it doesnt scare me at all though, the metal work is sorted and the point to point wiring is simply a matter or logic and pride in your work.  I fall flat on the theory of things and working out things like the OT (I opened up a hornets nest on this subject over at AX84 tonight)

Probably easier to PM anything else right now rather than fill the forum

[brett]

Hi
A really simple alternative is to buy a valve junior or small wattage amp off someone and add a power soak.  You can bring a valve junior down from 5W to a quarter watt with two resistors (3.3 ohm 5W and 1.2 ohm 1 W) and a switch:



cheers

[Papa_lazerous]

Thanks for that Brett, I am aware I could do that but then the tone will suffer big time, and I am a big believer in the saying "if a jobs worth doing its worth doing right"  hence the build.  plus its a dam good excuse to make something new 

[Pushtone]

I built the AX84 FireFly with Hammond transformers.
Total cost with a purchased chassis was $220.00 canadian.

It's the least expensive amp to build.
That makes it a good first amp build because any amp you build
will not be as good as the second amp you build. This is your first tube amp, right?

I the realm of 18watt kits, check out Brown Note.
http://www.bnamp.com/18wattlitekits.html

[phil]

Phil you say I can use the same PT & OT from the VJnr in the HeavyWatter??  I wasnt aware of that.  I am very interested in being able to make a heavywatter on the cheap and then as you say there is the possibility of making a firefly also..

Just following up on this - I did end up gutting my Valve Junior and converting it to a Heavywatter and I was able to use the existing PT and OT. The only things needed to buy were the tube sockets ($5), a 12au7 tube ($8.50), a handful of caps and resistors ($4). I had a 12at7 on hand so I used that instead of the 12au7 and I already had the caps and resistors so I only needed to buy the tube sockets. I've posted pictures in my gallery to show what's involved - the biggest issue was cutting the socket holes for which a unibit worked very well.

http://aronnelson.com/gallery/H3O-Jr-Valve-Junior-mod-to-HeavyWatter

The tones are great - very warm saturated tube sound when nearly dimed and the volume is bedroom level. There are a couple issues with the build though - motorboating when the gain is turned up 3/4 and the volume completely dimed. This would probably be fixed by adding a 47 - 100 mfd capacitor ($4) and a power dropping resistor ($1) just before the first stage (the voltage was 390 so I'm surprised the 12at7 wasn't red plating - B1+ should be around 280 or so). This should also take care of some 60hz hum issues from the PT.

Bottom line is that with a little more work the amp would make a great bedroom practice amp that would go from clean to crunchy. For me though I've already got another modified Valve Junior that will do clean to a little crunch at bedroom volumes so I want something that at bedroom volumes will sound more like a cranked Marshal amp so I am going to tear it down (except for the sockets and heater heater wiring), order a Hammond 125C OT ($20)  and turn it into a Firefly using point to point wiring with terminal strips. If I don't like the Firefly, I'll turn it back into the HeavyWatter. The Valve Junior was a great platform for converting - don't have to do the mains wiring (PT, Switches, rectangular plug/fuse connection already in place) or the cabinet and jacks are already there. The only 2 things to watch out for are: 1. the location of the existing 2 tube holes are about in the middle of the chassis which is probably not optimal so you'll probably need to cut new holes. 2. the existing standoffs are probably not where you'd want them so they may need to be removed depending on your layout and construction method (term strips, board).

[phil]

I want something that at bedroom volumes will sound more like a cranked Marshal amp so I am going to tear it down (except for the sockets and heater heater wiring), order a Hammond 125C OT ($20)  and turn it into a Firefly using point to point wiring with terminal strips.

I finished the conversion of the Valve Junior to Doug Hammond's Firefly using terminal strips for point to point wiring. This was my first point to point attempt, so it may not be the best layout, but it seems to work pretty well and was pretty easy to wire up except for the last connection on the terminal strip I used under the input switch. This was a great project for me as it was only the second the first non kit tube amp builds that I've done and the first Point to point project I've ever done. This also was my quietest (from a noise standoint) build so far.

Here's some pictures of the insides:

http://s95.photobucket.com/albums/l133/phil988/FireFly%20Jr/?

or Slide show version: http://s95.photobucket.com/albums/l133/phil988/FireFly%20Jr/?action=view&slideshow=true

Some build notes:

I added a 47uf 450v capacitor to the rectification stage to bring down the noise from the original Valve Junior's PT. Without this filter, there is noticeable PT noise. It's pretty quiet now, but making this a larger value (like 100uf) might be a good idea - the amp is quiet but when the volume is dimed, you can hear a faint buzz.

The undropped voltage from the stock Valve Junior PT after rectification was 386v so I used a 10k 10w (10w is probably overkill, but that's all I had that was over 5k) power dropping resistor which got me down to 211v on b1+ which I thought was too low, but the amp sounds great. A Value of about 7K would bring it closer to spec around 265V. I've got 4 27k 2w resistors, which I may try out in parallel as this would bring it down to 6.75k at 8watts which should bring it down to about 268V.

I still need to add a 220k 2w bleeder resistor, probably between the first filter cap and ground, and I may add a 1meg pot instead of the 330k resistor to act as a master volume.

I added 2 socket holes, 1 for the booster stage which I located near the input and the other for the output stage which I placed at the back, away from the other tubes and the preamp section. All tube sockets where mounted to the chassis as opposed to being on the PCB as in the original Valve Junior configuration.

The Hammond 125C that I used fit perfectly where the old OT was using the original mounting holes.

I used a lot of new components as I had previously used some components building ThunderTweak's Heavy watter but by resusing a lot of the original components, one would not need to purchase too many additional parts to convert a Valve Junior to a firefly. The following is a list of parts:

3 tube sockets and shields ($5 total)
1 Hammond 125C OT ($20) you can use the original PT with a dropping resistor and the original 4007's
1 100 mf 450v PT filtering capacitor ($3.50)
1 12au7 ($8)
1 12ax7 ($8) for the other 12ax7 you can use the original one.

18 ga solid wire for heaters

2 pots (boost and tone) ($3 total)
1 dpdt switch (boost switch)
1 power dropping resistor ($1) between 6.75k to 10k 10w.

handful of caps and resistors ($5)
Terminal Strips ($4)


Haven't had a chance to crank it up yet, but so far at very low volumes the amp sounds awesome ... definetly that Marshally sound I'm looking for so this is without a doubt a keeper. I can't wait to try this out with Doug Hammond's Highway 89 pedal ...

[MartyMart]

I took one of my removed VJ OT's and have used it for the heavy watter, running a 4 ohm
speaker off the 8 ohm tap will work fine.
It's still 3/4's done - other stuff got in the way, I have the circuit on tag board and just need to wire
PT/OT and off board stuff.
Hope to get to it in the next two weeks and will of course post pics and a sound sample

MM.

[geertjacobs]

The way to go for cheap tube amps:
non-diy
- Valve Junior
- Harley Benton GA-5
- somewhat more expensive but still good price/quality i hear: Orange Tiny Terror

diy kits:
If you're in England, check out http://www.ampmaker.com

[fikri]

Check this out ! http://www.diokay.com/forum/viewtopic.php?t=437

[stumper1]

http://www.diyguitarist.com/GuitarAmps/FireFly.htm

[Pushtone]

Check this out ! http://www.diokay.com/forum/viewtopic.php?t=437

That is one amazing amp ...

AND the rest of this site shows this builder from Indonesia has got skills.

Thanks for the link!

Check out the Custom page, wondefull pics.
http://www.diokay.com/custom.htm