Anyone else find Fender builds frustrating? (Blackface Princeton Reverb

[imaradiostar]

I've built a few amps- not 30 or 40 but enough that I feel like I'm half decent at it and I can be proud of my work and even sell an amp to someone every once in a while. I've built a bunch of different designs with trem and verb and varying amounts of gain and with a few exceptions I've always been able to track down the issues and make them sound good and look decent under the hood. I've even built a stereo twin based on a pair of blackface circuits and managed to get it to work correctly.

I've been building a Blackface Princeton reverb for my brother using a Weber chassis and board and I'm really frustrated! I feel like all of my layouts in the past have been really straightforward but this thing is not fun to build. I know Fender arrived at this design for a reason but I'm really not happy with it so far. I wish I'd skipped the Fender style board and built my own eyelet or turret board.

Anyone else ever feel this way?

jamie

[Tom Phillips]

Ever felt frustrated with a project? Yes.
But...the PR seems fairly straight forward and right in line with the complexity of many of the projects discussed here so I'm not really clear about what you are getting at.

[imaradiostar]

I just mean it's not my layout and I don't like it and it's frustrating to build relative to my own way of thinking. I agree, it's a simple single channel amp, not much of a challenge. I should probably shut up and just finish the thing but it's really bugging me.

jamie

[J M Fahey]

Fender layouts are usually very good; logical and clean.
The only (small) problem I find with them, is that they relied exclusively on axial electrolytics, while today radials are much more abbundant and cheaper to boot.
Anyway a drill and a few extra eyelets can solve that too.
*Now*, if that layout scratches you the wrong way, feel free to design your own.
There's nothing sacred about them.
Ooooops!

[imaradiostar]

I think there are specific things that bug me. On any of my amps I use 1/8 or 3/32 board material with eyelets or turrets and standoffs of a decent length. This allows any under board wires or transformer leads to not interfere with the board. The Fender style fiber board that came with the Weber chassis had eyelets in the wrong places (not a big deal, I pulled them out and keep Fender sized eyelets in stock) and the hole locations make it very difficult to mount the board to the chassis without shorting out against the eyelets. Once attached the board is bent over top of the transformer leads and doesn't lay flat against the chassis.

I decided against using a 4 or 5 section can cap so I'm using a two section cap for the first two filter stages and I'll use small easy-to package axials or radials with teflon on the leads for the other caps. It might look a little silly but I think it'll make for a quieter amp than a Princeton with a single can cap.

I work as an engineering tech and build a lot of mechanical and electronic assemblies. I've used turret board construction for a few high power circuits at work and my coworkers were impressed by how neat and durable they are. If I'd built something that looks like the inside of a Fender they would have asked why it looks like a rat's nest.

Sorry Leo, just calling it how I see it!

jamie

[Tom Phillips]

Jamie,

Sounds like you have two main issues.
1) The parts and materials supplied with the kit are lacking
2) Leo's original construction methods and grounding scheme can be improved upon.

Too bad about #1. From your description it sounds like there are significant issues with the kit.

I agree with #2. However, Leo's methods were appropriate for what he wanted to accomplish back in the day. I think there is a great opportunity to improve upon an old design such as the PR when you are building an amp for yourself. I really like the cosmetics of the blackface amps due to nostalgia reasons. However, if I were to build one today, the inside construction would not be a direct copy of the old methods.

Cheers,
Tom

[tubeswell]

Hi Jamie

I built a 6A14 kit in Nov/Dec 2009 but didn't get it working satisfactorily until July 2010. There were several issues, including what I deemed to be a bad cap can, poor pots, dodgy lamp holder and main board. I ended up replacing most of that (except the lamp holder, because I could get a standard fender lamp holder to fit), going to separate filter caps, made my own board and did the grounding as per Merlin's grounding article. JM2CW Keen to hear how you fix it. http://music-electronics-forum.com/t20860/

[imaradiostar]

Would it be a bad idea to mount the fiber board on standoffs? I'd add a few mounting points, of course.

jamie

[tubeswell]

Would it be a bad idea to mount the fiber board on standoffs? I'd add a few mounting points, of course.

jamie

I always use 'em, although hypothetically speaking, keeping wires close to the chassis is good for eating up any 'stray' EMF surrounding the wires - I guess it depends on your layout

[J M Fahey]

I find that particular fiber material too flexible for what you want.
Personally I buy 2 or 3 mm phenolic board, like phenolic PCB but unclad; at "electrical" (not electronics) shops, apparently they are used in electrical junction boxes or something like that.
They are far more rigid than fiberboard and (my reason to choose them), *real* insulators.
You might even get G10 glass-epoxy material .
These can be mounted safely on standoffs.
Hey! you may even use PC motherboard type ones; I bet Leo would.
Don't go on with your present board.
You'll "waste" a little time already spent, and will save a lot in the balance.
Of course, you may "base" your layout on the original one, it's "time tested" but sure can be improved.
Post pictures along your work and good luck.

[imaradiostar]

I pulled out an eyelet and moved it so I could use the stock mounting holes and bolt the boards flat to the chassis. It's a lot neater looking than a Fender so far but as we all know, neat doesn't necessarily mean it'll work correctly!

Here's a "work in progress" pic. I'll update as I approach completion. I need to get this done because I need my desk back to do schoolwork. It's too cold to work in my shop right now.



jamie

[imaradiostar]

I find that particular fiber material too flexible for what you want.
Personally I buy 2 or 3 mm phenolic board, like phenolic PCB but unclad; at "electrical" (not electronics) shops, apparently they are used in electrical junction boxes or something like that.
They are far more rigid than fiberboard and (my reason to choose them), *real* insulators.
You might even get G10 glass-epoxy material .
These can be mounted safely on standoffs.
Hey! you may even use PC motherboard type ones; I bet Leo would.
Don't go on with your present board.
You'll "waste" a little time already spent, and will save a lot in the balance.
Of course, you may "base" your layout on the original one, it's "time tested" but sure can be improved.
Post pictures along your work and good luck.

Yeah, I usually use the pretty colored G10-fr4 garolite from mcmaster.com. Sometimes I'll use the red swirly GPO from McMaster as well. It all depends on the look I'm going for and the turrets or eyelets for a given project. I have several thousand old military stock turrets- they look to be the same as the ones Dr. Z uses. They only work with 3/32" board so I tend to use the red GPO with those turrets. I have an assortment that fit mostly 3/32" and 1/16" board, some of which are tiny and perfect for really small layouts with modern caps like the blue ones shown in my picture above. I know some people claim cap mojo but I find picking the right cap values and careful layout have far more effect on the end result than using the perfect "vintage style" cap. I used the Mallory 150's in the signal path of this amp because I needed the lead length to span the eyelets.

Here are some of my other boards for works in progress:

[Tom Phillips]

Your in process PR work looks very nice. I can see that you are building in improvements too.
Cheers,
Tom

[imaradiostar]

Well, I've finished it. For all of my whining it really did turn out nicely. It's not as neat as I'd like but I still think it's cleaner and easier to troubleshoot than most Fenders. I used an LCR 50+50 cap for the plate and screen filters and a pair of 47uf radial caps for the next two filters, soldered to the buss wire on the back of the pots. I left the brass plate there but nothing is soldered to it.

It's dead quiet. Seriously. Quietest Fender I've played. I cranked it up a bit with a hotplate and it sounded great. The output tubes are idling at 40 and 47 ma per the 1 ohm cathode resistors. That's with ancient Sovtek 5881's- I'll probably put something nicer in it now that I've got it right. The trem is weak- do you think that imbalance is enough to cause it? I've not built any amps with bias vary trem before.

Please forgive the out of focus pictures.



jamie

[tubeswell]

Hi jamie

If its the 6A14 kit, the trem voltage is designed to wiggle 6V6 grids, and if you want to wiggle 6L6 grids, you need to change the voltage divider off the trem through the depth pot, to get a bigger voltage swing to feed to the 'bottom' of the 220k grid resistors. Either that or bias the 6L6s cooler. JM2CW