Upgrading an OT in a 5f2a

[newguitarsmell]

I have been using my 5f2a for bass for awhile now. I have a great speaker and I think that helps a lot. I am thinking about upgrading the OT so the amp is a little less flabby.
Right now it's a regular 5W single ended classic tone .. http://www.classictone.net/40-18115.html

If I upgraded it to 15W would that maybe help or??

Super dumb question: If I put a bigger OT in that 5f2a, do I need to change the values of any of the caps/resistors?

[jjasilli]

I suspect a solution is an audiophile grade OT.  See, e.g., https://www.lundahltransformers.com/tube-output/ There should be less expensive alternatives.


Mass manufactures of OT's for guitar do not expect a 5 watt SE amp to be used for bass guitar.  Probably OT frequency response drops off @ 100 Hz and below; but you want down to 40 Hz.  This is not likely to change with 15W SE OT for guitar.


But the hi-fi world provides OT options for low power SE with deep bass response.


It would be interesting to put .5 -to- 1 VAC signal into your amp @ 40 Hz.  Then measure it's voltage @ power tube G1; OT secondary & compute W output.  Then measure SPL compared to 1000 Hz.  SPL apps are available free for a smartphone.

[ginger]

Buy a Hammond 125-ESE , and replace your rectifier tube , with a solid state rectifier... OT mounting centers are different... like to drill
 ?

[SILVERGUN]

Listen to jjasilli and be very thankful that we have very knowledgeable guys who continue to hang around and answer a lot of the same questions over and over.
Ask yourself these questions:
- Why do I want to turn this tiny guitar amp into a bass amp?
- Why does jj suggest that I use an OT that has a rated frequency response down to 40hz? ...why 40hz?
- How big is my chassis and would it even be possible to use an OT that may or may not solve my problem?

And to answer your not-dumb question:
If I put a bigger OT in that 5f2a, do I need to change the values of any of the caps/resistors?
No, you can swap and listen at will as long as you take the reflected load into account
(Now, do you want to ask more about reflected load?)

Here is a SE OT that I used in one of my builds because I "had to have" better low end response:
https://www.tubesandmore.com/products/transformer-one-electron-output-1600-1684

Would it even fit?
Would it turn a 5F2a into a good bass amp?
No

[ginger]

Yes.. you need to increase the first cap ( B+ ) to 47 UF... IF , you change to solid state... i imagine , you have the fartiest  rectifier tube.. a 5Y3

[DummyLoad]

respectfully, but why? you're making maybe 5W. adding a wider response OT will require additional power to be of any use. IOW, 5W won't be of any use below 50-60Hz unless you play at VERY low volume, unless of course, you like gross distortion.

the flabby sonics are partly a result of open back cabinet and the rolloff of the (not made for bass) speaker you're using. try plugging into a closed back or ported cabinet. maybe that's all you really need to do?   


--pete

[ginger]

Well.. he's not telling us how he's using it... just him ,a nd an acoustic guitar ?

[ginger]

i'm surprised that no one is addressing the rectifier choice

[DummyLoad]

I have been using my 5f2a for bass for awhile now.

nothing states it's an acoustic. assuming it's just an electric bass.

---pete

[shooter]

I have been using my 5f2a for bass for awhile now

+1 for DL's suggestion, For future reference, JJ's Idea of UL is good to know.  I build mostly SE amps, 25W OT is about the practical limit, so I don't bother with smaller even when doing a 10-12W.  I also don't bother with tube Rec's.  a good OT should have multi taped secondary's, UL taps ~~ 40%

[sluckey]

I don't think throwing money at a 5F2A will ever make a decent bass amp.

[ginger]

Didn't suggest his bass was acoustic.. thought he may be playing , in an acoustic band,.. a duo ?!

[ginger]

     upright bass projects pretty well

[newguitarsmell]

YIKES!
Yes, I play electric bass. Yes at low volumes for lessons, never gigging.
No - I don't think I would ever be able to make a 5f2a sound like anything but poo by playing bass, but at the low volumes it's OK for lessons... and sounds better than the POS I have...

Would a new OT fit? Now that is a question..but I think so. Closing the cabinet I can also do.
I just want about 15% more tone - and never loud. Im playing it at 3 tops. It actually sounds pretty good now. I was just curious if I could tighten up the low end.

Thanks all for the comments!

[sluckey]

upright bass projects pretty well

Bet that ain't projecting through a 5F2A! 

[newguitarsmell]

Now Mr. Silvergun - thank you for always (or almost always) responding to my posts. I truly appreciate it. I am assuming the rating down to 40hz has to do with frequency response of the low bass strings.

Am I right?

I think I could put a bigger OT in there - with a wider response. It would be worth a try anyway. All it can do is sound crappy, a little better, or crappier! It actually sounds surprisingly good - except for the lowest notes.

It is super convenient to just use it as a bass amp. I have a keyboard amp that is awesome - and I think it works so well (not solid state - all tube) is because the OT is as big as the PT (physically). The response to the lowest notes of the piano in that amp are amazing. Both of those irons are MMs... and way too huge for a little 5f2a bug - - - but playing quietly, I think I could get away with it and sound decent..and experimenting is what it's all about.

[newguitarsmell]

I too am glad you all have patience to answer all the same questions again and again.

If I understand it all - in a nutshell - the "do'h" answer is - wider frequency of pitch, different makeup of OT....

[newguitarsmell]

And - what about the SS rectifier?
Change the first filter cap to 47uf? I really think we're onto something here....
 

[jjasilli]

I too am glad you all have patience to answer all the same questions again and again.

If I understand it all - in a nutshell - the "do'h" answer is - wider frequency of pitch, different makeup of OT....

Yes, there are good suggestions here.  But I still urge that scientific measurement is critical.  I.e., How much deep bass is actually getting processed inside your amp? How much is getting to the speaker?  How much is the speaker getting into the air? 


E.g., if 40 Hz signal is dropping off in the preamp -- not making it to the power tube -- then OT frequency response is superfluous.  Measure twice; cut once.


Re B+ filtering:  a good deal of bass guitar is below 120 Hz, the frequency of B+ ripple.  So a lot of filtering may be in order, in the range of 100's of uF.  See, e.g., https://sound-au.com/valves/clipping.html

[SILVERGUN]

Now Mr. Silvergun - thank you for always (or almost always) responding to my posts. I truly appreciate it. I am assuming the rating down to 40hz has to do with frequency response of the low bass strings.

Am I right?

Yes.
The lowest E fundamental frequency on a standard tuned guitar is 41hz, so you would wish for an OT and a speaker that would at least reach down that far

I think I could put a bigger OT in there - with a wider response. It would be worth a try anyway. All it can do is sound crappy, a little better, or crappier! It actually sounds surprisingly good - except for the lowest notes.

It is super convenient to just use it as a bass amp. I have a keyboard amp that is awesome - and I think it works so well (not solid state - all tube) is because the OT is as big as the PT (physically). The response to the lowest notes of the piano in that amp are amazing. Both of those irons are MMs... and way too huge for a little 5f2a bug - - - but playing quietly, I think I could get away with it and sound decent..and experimenting is what it's all about.

Ok...
I imagine that you were thinking of snatching up one of those Classic tone #40-18031er's. I like those and it aint the worst thing to get stuck with one.
I would expect that to sound marginally less crappy.
Changing to a SS rectifier will up your B+, giving you slightly more headroom, which might also result in a slightly less crappy sound.

Then, changing the first cap will slightly help the power supply to stay slightly stiffer under low frequency use.

Those three moves will reduce the overall crappiness of your 5F2a as a bass amp by a slight margin.
There is no mathematical equation for how much less crappy, so jj can't help you anymore. 

[SILVERGUN]

BUT, try to stay focused on what jj is saying...

If you are really trying to LEARN then the fact that he is willing to walk you through actual scientific testing is a huge testament to his graciousness and patience.

I'd take him up on it...and I have, many times

[newguitarsmell]

Thanks for all the help. OK jj... I have an oscilloscope and no idea how to use it to check these things.
Do you have a link for dumbasses that (ha ha dumBASSES how ironic) to let me know how to set it up and read the thing?
I can play some low notes through it and ??

And if I change the filter caps - lower them is what I am hearing - ..golly maybe this is above my ability.

[SILVERGUN]

Thanks for all the help. OK jj... I have an oscilloscope and no idea how to use it to check these things.
Do you have a link for dumbasses that (ha ha dumBASSES how ironic) to let me know how to set it up and read the thing?

I have posted a pdf for general setup, but there are some things that you will need to wade through in order to get to the other side
A link= www.google.com

I can play some low notes through it and ??

Once you learn how to use it, you will actually be able to see the amplitude of different frequencies.
It is a beautiful site to behold. Seeing something that normally can't be seen.

And if I change the filter caps - lower them is what I am hearing - ..golly maybe this is above my ability.

If you lower the values  (which is the opposite of what we have suggested), it would result in less power supply stiffness and less ability to deliver solid low end.

Maybe it is above your ability, maybe not.
Only you can determine how much you want to learn, are capable of learning, and/or how much you actually need to know to accomplish your goals.
Try to stay focused on one issue or suggestion at a time and work towards a specific goal....i.e. swap in the less crappy OT and see if you can tell a difference....or not

"If you do nothing, nothing will get done" - Me 2019

[jjasilli]

Scope is good to learn, but not needed here.


All you need is a volt meter; signal generator & SPL meter.  The latter 2 can be apps on your smartphone.  Put a 40Hz signal into the amp.  Use a voltmeter to set the input signal voltage.  Maybe go through the process at 3 separate input voltages: 200mV; 500mV; 1V.


Then measure the 40 Hz signal voltage at the power tube input (G1).  The vol control should be full up. Turn down the input voltage if there's audible distortion.  Take voltage measurements with the tone controls at 0, 12 o'clock & full up.


Measure the OT output voltage into the speaker with a voltmeter.  Measure the SPL of the speaker output.  Write down all of these measurements.


There are web tutorials for all of this.


Repeat the process at 400 Hz & at 1000 Hz. Then you'll really know how the amp / speaker are performing. 

Alternatively, some of these things could be modeled in SPICE; but I don't know how to do that.

[ginger]

upright bass projects pretty well

Bet that ain't projecting through a 5F2A! 

Yeah .. meant  a stand-up bass would project better , than running one through a 5F2-A

[ginger]

Running a bass through a 5F2-a  is  not bass-like, although , thanks for people who try weird things

[newguitarsmell]

This is the OT I am going to try. We'll see what happens.