5f2a

[newguitarsmell]

Hi guys,
Quarantine has driven me back to my shop. I have been reworking and rewriting projects and I feel like I am starting to better understand all the stuff you guys helped me with. I will tell you this - I have made three amps and each time they worked fine at startup. My soldering is cleaner - etc.
I rebuilt a little 5f2a in a champ chassis I had. It sounds great - breaks up pretty early though. I'm thinking of swapping out the 12ax7 for something else?
What else can I do for more headroom? Two questions specifically.
1. How do the values of the coupling caps effect the tone/overdrive (maybe this is what you call "flabby".)
2. How can I better focus my preamp section to get more headroom?

Gonna try some different preamp tubes tomorrow.
Thanks.

 

[echuta13]

Maybe try a 12AY7 or 5751 in the preamp?  I put a coupling cap switch in my 5f2a's that give me the option of a .022 cap or a .0047.   The 5M resistor across the switch is to prevent a pop.

[DummyLoad]

disconnect cathode bypass cap on 1st gain stage. disconnect cathode bypass cap of 6V6. as already stated: swap 12AX7 for lower mu tube, e.g., 5751 ; 12AY7 ; 12AU7.

12AY7 is going to suck more current with resistor values fender used (100K Ranode + 1.5K Rcath) so B+ for the preamp tubes will drop somewhat.


5751 with 1st stage cathode bypass disconnected may work out best for you.


--pete

[Leevi]

Change the 10K resistor between 1st and 2nd filter stage to lower e.g. 5K-1K.


Use more sensitive speaker.
/Leevii

[shaun]

I'd try and find a Decade box online and experiment/tune the amp until you get the sound you like. You can get a decade box for resistors or for capacitors (different boxes). You hook the cap decade box in the place of the capacitor in question - say, the cathode cap - and try the various caps with the turn of a knob until you get the tone you want.
Just a thought.

[newguitarsmell]

disconnect cathode bypass cap on 1st gain stage. disconnect cathode bypass cap of 6V6. as already stated: swap 12AX7 for lower mu tube, e.g., 5751 ; 12AY7 ; 12AU7.

12AY7 is going to suck more current with resistor values fender used (100K Ranode + 1.5K Rcath) so B+ for the preamp tubes will drop somewhat.


5751 with 1st stage cathode bypass disconnected may work out best for you.


--pete


I removed the cathode bypass cap going to #3 of the preamp tube. That helped a lot. Didn't have a 12ay7 - so I used a 12at7 which brought the volume down, but not so much the quality of tone.
I disconnected the bypass cathode and it sounded a little better.
My B+ filter cap is a 33uf/475v. Should I lower that?
A regular champ calls for one 16uf and two 8ufs... the princeton calls for the 33uf and two 8ufs. What do you think?
The amp sounds good - no hum or anything - just feels overdriven, still. I have an extra choke I could try but where would I put it?

[DummyLoad]

with no cathode bypass caps installed, the dynamic range of that 5W amp is about a good as it's going to get.  power supply doesn't need smaller caps - if anything you'd want to shave low frequencies by using smaller value coupling cap between the two preamp triodes - there's a .022u there now, if you built stock 5F2A - try a .01u or even smaller .0047u. low frequencies require more power, so try that approach.     

if you need more "headroom" than what you have now, what you really need is more power or, as already stated, you could try a more efficient speaker.



--pete

[newguitarsmell]

What power transformer should I upgrade to? Just have a classic tone Champ PT in there now.
Will that give me more headroom?
Trying with a different speaker today.

[sluckey]

I'm reminded of silk purses and sow's ears. What you need is another amplifier, something with more oomph, and headroom.

[DummyLoad]

seriously, you have a 5W amp, no bypass caps and as much headroom as you're going to get. swap PT and MAY get literally ONE more watt out that poor little 6V6, so little you probably won't notice the change and will have wasted $80 + freight on a transformer.

you need to move more air for more headroom and that will require more power to the speaker.

build the attached, it has more headroom than a twin reverb into a pair of JBL or EV12L speaker(s). it sounds so sweet, you'll need insulin shots. 



--pete

[newguitarsmell]

Pete!
I will. Can you help me out with a layout?
Awesome

[DummyLoad]

Pete!
I will. Can you help me out with a layout?
Awesome

if you give a first shot at it, i will help. hint, start by modifying a similar fender plan: study a deluxe 5E3 and graft in the differences + you have 4 output tubes instead of 2. 


--pete

[newguitarsmell]

Hi Pete
I'm going to give it a shot but it might be above my pay grade. Message me please, if you'd do it for a fee. I know some things from this schematic, but have to start teaching school again here soon so ...

[DummyLoad]

i was going back through my notes, and i noticed that i have the wrong choke indicated on the rev. 2.0 schematic - i actually used a hammond 3H 500mA, specifically the model 193N for this 4x EL34 output stage. i corrected the schematic and changed the rev to 2.0a. i will unlink in the previous reply. my apologies for any confusion and the oversight.

use this schematic as i believe it reflects what i used in my experiments. i used salvaged carvin transformers as indicated in the schematic, the other part numbers listed should work close enough to not need any adjustments to the circuits.

working on a layout.     


--pete 

[2deaf]

What does the "Cut" control do?  It looks like it won't do much until VR4 is under 20K or so.  When shorted or nearly shorted it looks like it might be a high cut filter. 

[DummyLoad]

What does the "Cut" control do?  It looks like it won't do much until VR4 is under 20K or so.  When shorted or nearly shorted it looks like it might be a high cut filter.

yes, high cut - not a fan, yes shaves highs and not a good way. why i didn't bother breadboarding it.


--pete

[newguitarsmell]

Awesome. Tore apart a couple of amps I built months ago and am rebuilding them from scratch. I figure the more I build, the better I will get at it. . so far so good.
Looking forward to the layout.
M