59 bassman 5F6A build

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Delmar Evans
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59 bassman 5F6A build

Post by Delmar Evans »

Hello. Just finished 59 5F6a build. Sounds great with excellent tone. However, it does not seem very loud. Running National 5881 tubes, biased at 38ma, 12Ay7 in V1, 12Ax7 in V2 and V3 , GZ34 rectifier. Plate voltages at 424 VDC. Mercury magnetic HT and OT and Choke. I was comparing the volume to my Super Reverb as I was using the 4 10inch speakers in that cabinet . Seems like a much quieter 40 watt amp than my Super. Any thoughts appreciated.

Delmar
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M Fowler
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Re: 59 bassman 5F6A build

Post by M Fowler »

Delmar,

Must be something wrong because my Super Reverb and 59 Bassman are both loud amps with more then enough headroom for gigging.

Hope you can figure it out.

Mark
pdf64
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Re: 59 bassman 5F6A build

Post by pdf64 »

Might the perceived volume discrepancy be due to differing overall gain levels / volume pot tapers (the conformance to the nominal taper is unlikely to be a specified parameter)?
Ignore the numbers and just tweak the tone and volume controls to get both amps to a similar tonal balance and at their max clean volume; do they both now create the same sound pressure level, when used with the same speaker cab?
stretch2011
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Re: 59 bassman 5F6A build

Post by stretch2011 »

Hmm my 5f6a build is freaking loud. Although I don't have a super reverb to compare it to. Side by side it Is roughly twice as perceived loud as my tweed deluxe. But that's 28w vs 12w.
danman
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Re: 59 bassman 5F6A build

Post by danman »

There is a 470ohm resistor in the PI between the two 1meg resistors. Check to be sure that you do have a 470ohm and not a 470k installed by accident. This happens occasionally on new builds and will cause the amp's volume to be much lower than it should.
Delmar Evans
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Re: 59 bassman 5F6A build

Post by Delmar Evans »

Thanks for replies. I did check the 470 ohm. It is the correct value. In addition , I'm running a 12ay7, 12ax7, 12ax7, 5881, 5881 and a GZ34 in this amp. Plate voltage at 425 VDC and Bias set at 70% of 23 watt dissapation tubes for a value of 38ma. All voltages throughout seem normal. Another thing I notice is that the volume on either channel does not start to respond until you hit "3". Don't get me wrong, the amp sounds great and maybe I expected more volume. I'm running 6L6gC and 12ax7 in my Super, so maybe that is not a fair comparison. Also coupling caps are PIO Russian
Delmar
pdf64
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Re: 59 bassman 5F6A build

Post by pdf64 »

Delmar Evans wrote: Don't get me wrong, the amp sounds great and maybe I expected more volume.
Do you mean gain or sound pressure level? eg does it get as loud as the SR if turned to 10, if not, how about if a clean boost pedal was used as well?
Delmar Evans wrote:Another thing I notice is that the volume on either channel does not start to respond until you hit "3"
This could just be the particular tack taper; what are the pot's brand / vendor?
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rp
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Re: 59 bassman 5F6A build

Post by rp »

Your 5F6A has a 2 ohm tap? You built a real deal 4X10 in series combo style tweed Bassman? Have an OT with 2,4,8 taps or did you rewire the SR speakers? I'm sure you are onto the output impedance issue but never know.

My 5F6a is the same as your 425V with NOS 5881 and it's loud - but I don't really know what loud is anymore, I'm an old fart.
Delmar Evans
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Re: 59 bassman 5F6A build

Post by Delmar Evans »

Yes , real deal 2 ohm 4x10 all in parallel. Speakers 1968 fenders 1 meg cts volume pots all other pots alpha. It sounds great. I can sit in front of it with volume at 6-8. Cannot do this with my SR. So in reply to the other question , yes this is a sound pressure comparison not a gain issue. I've never plsyed out of a tweed bassman so I'm not familiar with how a 5881 tube is as compared to my SR with 6L6 GC tubes in it.
Delmar
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rp
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Re: 59 bassman 5F6A build

Post by rp »

I could sit in front of a SR at 8 :lol: A tweed Bassman w/ real 5881s is not as loud as a SR with real 6l6GCs at prolly ~ 450V, but not by much, hard to tell this over the internets, one man's "turn it down" is an other man's "turn it up". But maybe something is not right.
pdf64
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Re: 59 bassman 5F6A build

Post by pdf64 »

If you turn it up to ten does it get loud enough?

How about with a 12AX7 in V1?

The point I'm trying to get across is that the number on the dial required to achieve a particular output is irrelevant to the system's performance.
It's just a user interface thing.

The stock volume pots on your SR are likely a ~30% taper.

The standard CTS audio taper is usually 10%.

A setting of 6 means nothing in the face of that.
Delmar Evans
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Re: 59 bassman 5F6A build

Post by Delmar Evans »

I have not tried a 12AX7 in V1. I agree , I may be overthinking. The amp sounds great, and yes , it does get loud enough. Thanks guys for all the input. Maybe a sound clip is in order!
Delmar
Teleguy61
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Re: 59 bassman 5F6A build

Post by Teleguy61 »

Sometimes "It's not loud enough" means not as punchy as expected, or not as much headroom as expected, not really a volume issue.
Are you saying it doesn't feel like you thought it would when you play it?
Delmar Evans
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Re: 59 bassman 5F6A build

Post by Delmar Evans »

Maybe it's just a "feel" issue. Not sure. Give it a listen.

http://youtu.be/BJOw_ewpTco
Delmar
strelok
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Re: 59 bassman 5F6A build

Post by strelok »

After listening to your clip (which sounds very nice btw :D ) it seems to me like the most likely issue is that somewhere in the amp signal is not getting passed at the level it should. Most likely the preamp. I've never experienced a real 5f6a bassman in person but from listening to clips online and having experienced similar circuits my intuition tells me you should be getting a lot more breakup with the volume at 8. Does it get much louder or more distorted as you turn it up all the way? Unless of course you're using really low output pickups. Have you tried it with humbuckers?

The reason I say its in the preamp is that if it was an issue with the output I would think you'd be getting a lot more overdrive than you are just from the preamp at that point. With the volume maxed you ought to be into some pretty good overdrive.

I would go through the amp and make sure the resistors are all the right value and the wiring is all correct. Check the solder joints too, it could just be a bad joint thats not conducting well. If you have a signal generator and scope you can trace the signal going through the various stages and it will generally become apparent where the problem is.
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