Looking for guidence/suggestions - an 18watter in a pro jr.

[DeanOwens]

i posted this on the ax84 but didn't get much help. i saw about a year ago where someone built an 18watter in a projr. chassis and cab and thought it was pretty cool. it looks like i will be getting a broken pro jr. for a good price in the near future and was thinking about doing the same.

here's the problem - if you've seen the pro jr. you know there is one input. i'm looking at building the lite II but i have to figure out what to do with the other triode. i can ...

1 - waste it by not hooking it up
2 - run it in parallel
3 - set up the 12ax7 kind of like a 5F1 with the volume between the two for more grit
4 - ?

any suggestions? someone on the ax84 suggested possibly using a push/pull pot and have...
push - to be #1
pull - to be #3 of some sort.
my only problem is i'm not sure exactly how to do that.

let me know your thoughts.

[zaphod_phil]

Hey, guess what, there's a lot of the same nice folks here, as on the AX84 BBS!

My vote is for the parallel triode option (#3). Easy as falling off a log, and you get more gain if you keep the same anode load resistor value, or less noise with teh same gain, if you halve the load resistor value. Most folks agree that the parallel triodes help fatten up the tone some.

Meanwhile, Loverocker, has posted his 18W clean boost circuit, on http://www.firstmail.com/18w/cleanboost.gif

Is there really no space on that panel to drill just one little hole??

[DeanOwens]

Hey, guess what, there's a lot of the same nice folks here, as on the AX84 BBS!

yeah. i've always thought it was funny how there are all these boards and it seems like everyone visits them. what i was trying to say was that maybe this would get a little more attention over here since it's just an 18watter site as oposed to a site that deals with so many other homebrews.

My vote is for the parallel triode option (#3). Easy as falling off a log, and you get more gain if you keep the same anode load resistor value, or less noise with teh same gain, if you halve the load resistor value. Most folks agree that the parallel triodes help fatten up the tone some.

thanks for your input. i think this is where i'm leaning. but not real strong. i probably won't get to building this for a few weeks but i'm the type that likes to do his research well in advance.

Meanwhile, Loverocker, has posted his 18W clean boost circuit, on http://www.firstmail.com/18w/cleanboost.gif

Is there really no space on that panel to drill just one little hole??

i saw that and i like it but space really is an issue. take a look at the link http://mywebpages.comcast.net/tweeddelu ... shall.html that got me thinking about this and you can see from the pics that there's not a lot of room on that faceplate.

i was thinking of possibley using a sterio input jack for the boost link you provided but it looks like he also uses another pot. maybe i could just put a fixed value in.

still thinkin'

[Plexi]

Heres the link to the Jr.. may get some ideas.
http://mywebpages.comcast.net/tweeddelu ... shall.html

There are some good circuts to use for an amp like that ..and they can be simple and suprise people on how they sound. I've converted a couple small gibson amps into amps similar to this. It depends on how or what you want to get out of the amp. If its more gain or what..or a balance between them.

Richie

[DeanOwens]

...It depends on how or what you want to get out of the amp. If its more gain or what..or a balance between them.

Richie

there in lies the rub. i'm not sure what i want. in an ideal world i would i like to have the ability to have the normal 18watt sound and one that is pushed a little more. as far as amps go, i'm pretty mixed up. i grew up playing metallica and like that crunch but now i play a tele in a church praise band (hope that's not illegal to mention that here) so i obviously don't play with that much crunch any more. i've also really gotten into classic rock in the last few years. so i'm really all over the map. that's one reason i got into building. i know that one amp won't cover every voice. this one might cover a few but not all. so i'm looking for the best i can get out of it. not really all the crunch i can get out of it. and because i use a tele, i was thinking of running the triodes in parallel. the more i think aobut it, the more i'm leaning that way.

[loverocker]

OK, if you don't want to drill holes - and *that* is a tiny panel! - how about this:

Phase I: wire up a parallel triode like on the Lite II, but instead of using two jacks, use the jack you have, but use a push-pull on the Volume pot to switch between single and parallel. If that doesn't have enough gain for you, go on to...

Phase II: Move the push-pull to the Tone pot, and use a dual-pot in the Volume position. Then wire for cascaded triodes (i.e. that simple triodes in series thing I posted), and change the push-pull wiring to let you switch from inputing into the straight 18W circuit or the cascaded circuit.

You spend a bit more on pots this way, but keep the panel as is.

[Aaron]

dean,

first of all, i'm glad someone else is doing this - it's an absolutely great idea that i'm actually thinking of doing if i can get a cheap/broken pro jr. where/how much did you get yours?

sound and tone-wise, if you use a distortion pedal in front of this amp you can definitely get metal tones. you might want to make it a closed-back cab though in order to get that bassy thump for palm mutes. have you considered that? it doesnt look too difficult...

also, are you going to to use the SS rectifier or install a tube in there?

-Aaron

[DeanOwens]

OK, if you don't want to drill holes - and *that* is a tiny panel! - how about this:

Phase I: wire up a parallel triode like on the Lite II, but instead of using two jacks, use the jack you have, but use a push-pull on the Volume pot to switch between single and parallel. If that doesn't have enough gain for you, go on to...

Phase II: Move the push-pull to the Tone pot, and use a dual-pot in the Volume position. Then wire for cascaded triodes (i.e. that simple triodes in series thing I posted), and change the push-pull wiring to let you switch from inputing into the straight 18W circuit or the cascaded circuit.

You spend a bit more on pots this way, but keep the panel as is.

sounds good. i think that's what i'll do. the only thing is, i'm not sure if i know how to do it.

let's take phase I - would i hook up one side of the volume pot to the last triode and the other side of the pot to both? is it that simple? i don't have anyway to post a schem so i hope that makes sense.

phase II - this one is giving me a lot more trouble in my head. i need to sit down with a pen and some paper. also, if i remember correctly, the volume pot for the 18watter is 500k and the pot you show for that boost is a 1meg. would it make a difference either way when picking the dual ganged pot? i'm guessing it would be best to just get a dual ganged 500k.

[DeanOwens]

dean,
...where/how much did you get yours?

i saw the "farshall" about a year ago and have just been "lightly" looking for one that was down. on one of the boards that i visit i saw a thread where someone was asking what happened to their pro jr. they said they were going to have a friend look it over. i sent them a note saying that if they don't want to fix it, could i buy it. i got a note back that said that their friend didn't want to waste his time with a pcb and to make an offer. i offered 100.00 and they said that's fine. even if you got one off of ebay that was working it wouldn't be a bad price. i've seen them go for 180.00 on ebay. when you figure you get everything and all you have to do is change out the board and get some tube sockets, it's a pretty cheap way to get a little 18watter.

...sound and tone-wise, if you use a distortion pedal in front of this amp you can definitely get metal tones. you might want to make it a closed-back cab though in order to get that bassy thump for palm mutes. have you considered that? it doesnt look too difficult...

i'm trying to make myself pedal-less. i know i might have to use one but it would be great to only have to cary an amp and a guitar.
and i'm not sure about a closed back. first off, it's a combo and the tubes have to be able to breathe. second, the ones i've seen are pretty close to closed already. i'll probably build an extention cab that will be closed back.

also, are you going to to use the SS rectifier or install a tube in there?

i'm still thinking through this one. the 18watt schem i have shows 325 after the tube recto. the 18watt lite schem i have shows 305 after the recto. the pro jr. schem i have shows 319 after the ss recto. i'm not sure how much the difference in voltage would matter to the sound. i've thought about contacted ted weber and looking into a copper cap. if i remember correctly, you can specify how much voltage drop you want and how much sag you want (basically a costum recto) for the same as the premade copper caps. plus, i think it has a delayed start up to help in amps that don't ahve a standby.

as i get further in this, i'll let you know. but that could be a while. i'm job hunting and i have to put building on hold until i can get a pay check coming in.

[loverocker]

let's take phase I - would i hook up one side of the volume pot to the last triode and the other side of the pot to both? is it that simple? i don't have anyway to post a schem so i hope that makes sense.

phase II - this one is giving me a lot more trouble in my head. i need to sit down with a pen and some paper. also, if i remember correctly, the volume pot for the 18watter is 500k and the pot you show for that boost is a 1meg. would it make a difference either way when picking the dual ganged pot? i'm guessing it would be best to just get a dual ganged 500k.

Dean - Not sure I was clear: I was talking about using a DPDT pull pot where the pot's lugs are wired exactly as per the Lite II schematic, and the switch's lugs dictates whether one or both sides of the first valve get the input signal. I'd have to scratch this stuff out on paper to work out which wire goes where though. Let me try to scratch something out in the next day or so.

Yeah - a 500K dual pot would be fine if you wanted to try Phase 2.

[DeanOwens]

Dean - Not sure I was clear: I was talking about using a DPDT pull pot where the pot's lugs are wired exactly as per the Lite II schematic, and the switch's lugs dictates whether one or both sides of the first valve get the input signal. I'd have to scratch this stuff out on paper to work out which wire goes where though. Let me try to scratch something out in the next day or so.

Yeah - a 500K dual pot would be fine if you wanted to try Phase 2.

i'll be honest (which is always a good thing), i have only been reading about this stuff (tube amps specifically - i have other electronics background) for a little over a year and my building experience is somewhat limited. i've basically built a vibrochamp, a 5E3, and i've done a cap job on a blackfaced tremolux. all of which are simple with no switching or push pull pots. i'm not a morron but i've never had to use them. if i saw it on a schem it would probably be easier for me. so any help you can give me would be great.

[jetsetscoot]

Dean-

You may want to email Tom S who did the Farshall conversion - he was fairly active in the old 18W yahoo list. I emailed him and he ended up doing an 18 conversion for my Pro Jr. He used the original fender trannies and wired an SS rectifier, but other than that followed the 18W lite circuit. I built a 2x10 combo cab for it and have used it is numerous small gigs.

BTW - I still have the perfectly functional guts from the Pro Jr. and have no intention of putting them back in. If you change your mind and want to just repair your broken fender I'll sell 'em to ya cheap.

-John

[Aaron]

a push/pull pot is simply a pot attached to a switch - usually a DPDT. basically if you have the shaft facing up, there's the normal pot, and underneath that an enclosure for the switch. when you pull up on the shaft of the pot, it throws the switch. there's no internal connections between pot and switch, they're just attached for convenience - like now when you dont want to or have no room to drill a new hole...

hth

aaron

[DeanOwens]

You may want to email Tom S who did the Farshall conversion...

i've thought about that, just haven't gotten around to it. i'll email him tomorrow and see what he has to add to the topic.

BTW - I still have the perfectly functional guts from the Pro Jr. and have no intention of putting them back in. If you change your mind and want to just repair your broken fender I'll sell 'em to ya cheap.

i'll keep that in mind. not sure if i'll take you up on it though.

[DeanOwens]

a push/pull pot is simply a pot attached to a switch - usually a DPDT....

do you have a mouser part number or know where i can get one? i thought it was somehow two pots in one (up ingaged one while down it was the other). i was wondering how that would work. with this switch, would i just hook up say the plate or cathode of the boost to the switch so when it's off (down) the tube is "shut off" and when the pot is up it would connect the plate to the voltage or the cathode to the cathode resistor to connect the curcuit?

with that, how do i switch the grids? what i mean is, on the 18 watter the input goes straight to the grid. but on the boost the input goes through a 68k grid leak resistor. would i just use the switch to go back and forth from the different grid? i'm so confused

[DeanOwens]

i'll go ahead and put this here. if i don't get any answers then i'll start a new thread.

assuming i do the boost that loverocker posted http://www.firstmail.com/18w/cleanboost.gif in the first triode of the 18watt lite II http://www.18watt.com/Storage/18wattLite2.gif i have some questions.

R3 - does it stay 100K
R4 - does it stay 820
C1 - does it stay 50/50 or does it get knocked down to a 25/50

questions unrelated to the boost

R8, R13, & R14 have an R after the value rather then a K or nothing like R4. is this a typo or something i'm not aware of?

i've been told that R5 can be changed to a 47K - what difference would this make tone wise?

i think that's all i have for now other then trying to figure out how a stinkin' p/p pot works.

thanks for the help you guys have been so far. i do appreciate it.

[zaphod_phil]

questions unrelated to the boost

R8, R13, & R14 have an R after the value rather then a K or nothing like R4. is this a typo or something i'm not aware of?

i've been told that R5 can be changed to a 47K - what difference would this make tone wise?

i think that's all i have for now other then trying to figure out how a stinkin' p/p pot works.

It's conventional to put an R after the value if it's in ohms, rather than in thousands (k) or million (M). Or sometimes the value is written without anything after it all, in which case it's again in ohms. Most of us just don't have the Omega symbol on our keyboards.

The 47k is from the earliest original 18watters. It should give a little bit more clean headroom as well as drive to the power tubes. Some folks therfore say the amp sounds 'airier' with it in.

There's nothing to a p/p pot. It's just a regular pot, with a simple switch on the back, which opnes or closes depending on whether the dhaft has been pushed or pulled. Very simple. and convenient

[Aaron]

dean

look at http://www.mouser.com/catalog/615/368.pdf it's in box "D" right at the top.

i'm not sure on the circuitry you're trying to do, but it seems like you need two switches in one. the DPDT will do it - one side applying voltage to the tube, the other side switching grids....

aaron