5f2 problems

[brian newman]

I put together a 5F2 about a year ago.I used the updated schematics from
Steve's DIY Guitar amp pages.
I've had an ongoing problem with,for lack of a better term speaker breakup
at the lower frequencies.I've tried a number of different speaker eg.a pair of
8"alnico Heppner,8" sammi sound to a vintage 15" phillips driver.
They all have the same breakup at lower frequencies.This breakup I speak of is not the muchsought after tube sound.I know that many believe that anything smaller than a 12" just doesn't cut it,but would like to know if anyone has built for the same schematics and experienced the same problems.
I'm looking at a vintage 30 on ebay but I would hate to buy another driver to only have the same problem.
Als0 this amp has a hum to it any proven tweeks to fix this problem


Thanks Brian

[MWJB]

Can you describe the low end "break up" & how it sounds/differs from other Champ/Princeton amps that you have heard. If all speakers you have tried are affected, it is unlikely that it is a speaker issue.

Hum - there are numerous causes, can you isolate it to a particular stage? Pull the preamp tube, does it still hum? Check for grid wires lying too close to plate/heater wires.
Does it sound like a ground loop hum? If so, that's what it might just be.

[petemoore]

I re-read through a number of posts that had collected in 5e3, your favorite tweeks thread.
I got the schematic and started at the input jack.
I didn't understand Fender input sectiona, and had put 1 input jack.
Between having a cathode ground tied to support [connected it to unused'' input jack], seriously screwed with turning the amp up, and bass notes suffered worst, but not having a great 5e3 to compare, the suffering was of a type which I didn't immediately recognize.
Lifting that ground let the amp turn up 3 times as loud without the 'wierdness'.
Raising a grid bias resistor from 68k to 1 meg certainly helped also.
Getting all that straightened out then making the coupleing caps in the pre-amp smaller made this amp rock up one side and down the other for the first time.
Of all the times I said "I got it right now' I think I got it right now...lol.
When I first got output, someone here told me "There's more to it than just getting it going, you have to make it Purr, that can take some effort}...and he was right...at the time I was thinking 'what the heck does that mean'.
Anyway now you've heard the dumm mistakes I made on first amp build...one little wire 'wrong', or something else can take otherwise great amp and reduce it to 'an amp that 'works'.

[brian newman]

Thanks for the reply
I will try your suggestion today and report back.
I'm fairly new to electronics so it's all a learning curve for me.
I purchased a Celestion G12-30mg for 20 US on ebay so I hope this will help the sound somewhat.I hope it fits,I may have to shift something to make it fit.If I build another amp I'll increase the cabinet size to accomidate a 12" driver
I do believe I have the wiring done as per schematics but I'll run through it again.

Thanks Brian

[sportster4eva]

I put together a 5F2 about a year ago.I used the updated schematics from
Steve's DIY Guitar amp pages.
I've had an ongoing problem with,for lack of a better term speaker breakup
at the lower frequencies.I've tried a number of different speaker eg.a pair of
8"alnico Heppner,8" sammi sound to a vintage 15" phillips driver.
They all have the same breakup at lower frequencies.This breakup I speak of is not the muchsought after tube sound.I know that many believe that anything smaller than a 12" just doesn't cut it,but would like to know if anyone has built for the same schematics and experienced the same problems.
I'm looking at a vintage 30 on ebay but I would hate to buy another driver to only have the same problem.
Als0 this amp has a hum to it any proven tweeks to fix this problem


Thanks Brian

Since it's a pretty simple circuit, my guess is the hum is probably a combination of filament wiring, and (correct me if i'm wrong) since it's a single ended princeton, I would say power supply filtering. The last one I did I used a choke between the first filter stage and the second, and took b+ from the second node. quiet all the way to 12. The nasty breakup you hear could be a combination of things. What kind of output transformer are you using?

[brian newman]

To post a picture on this forum do your pictures have to be web based or can you upload them direct from your hard drive.
I removed the preamp tube and the hum was reduced a little but still there.
I moved some wires around while it was powered up and I didn't notice any change.I didn't have alot of time today to get more indepth.

Thanks Brian

[brian newman]

Ok I figured out how to upload a pictures.
While I was organizing my bench I realized that This amp is built from The schematics off of
Angela Instruments 6V6 single ended schematics.I guess I have too many schematics on my bench.
Sorry for the error I guess I shouldn't let these projects slide for six months.
The only thing I did different from schematics was 22uf x3 for power filters(instead of 16uf)and a toggle switch for the OT impedence as I couldn't make my mind up what impedence to use off the Hammond 125ESE


Thanks Brian

[brian newman]

Here's a few more detailed pictures of the wiring.
I checked the wiring again for loose connections and proper wiring.I reread the Angela instuments page on this design and the feedback suggested that this design is noisy when using nonshielded wire.
I do have some teflon wire on hand so can anyone tell me the most effective places to use it.
Better quality filter caps will probably help also

Thanks Brian

[Gee]

Hi Brian,
Your problem could well be caused by lead dress.

I can see that it looks like your are using the chassis for one side of the filament supply. I know that Leo did it that way but I bet there was a lot of trial and error on the way. A far better way is to add a second filament wire and create an artificial ground between the 2 with 2 100R resistors to ground (assuming you don't have a 6.3V center tap). This will help greatly with hum.

The other thing I notice is that the area between the 6V6 and the board is very crowded. I would add another chassis hole under the speaker jack for the speaker wires. That should reduce some of the crowding and allow you to chopstick the leads about to see if you can eliminate the problem.

Good luck.

[brian newman]

Thanks Gee
By crowding between the board & 6V6 do you mean space or amount of wires.
The extra wires are from the OT,as I stated before I couldn't make my mind up on which impedence to use,I will remove the extra wires.

Thanks Brian

[MWJB]

What rating is that 6V6 cathode resistor, I'd use 5W there, 2W would probably be OK, but yours looks like 1/2W?

Remount those 68Ks on the input jacks and run shielded wire from the jacks to V1, 2, do the same from the vol pot to V1, pin 7. I'd do the same with the grid wire going to the 6V6 pin 5.

I notice you don't have a 25/25 bypass cap at V1, pin 3? Most Champs & Princetons had this cap.

You could go up to 40uf at the main B+ filter cap, see if that helps the hum, as well as Gee's suggestion.

Separate the preamp & screen supply filter cap grounds & ground the preamp stuff at the input jack.

I'm not crazy about that red DC wire feeding the preamp plate resistors, run this behind the board, or use solid core wire and stand it up high away from the components rather than trailing loosely.

[brian newman]

MWJB thanks for the imput I did everything you suggested except reroute the
red DC wire.
Boy what a difference,the hum is almost gone at least to the point that I can live with it.

Thanks again Brian