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5F6A clone too bassy


 
8/31/2005 1:30 AM
Rene 5F6A clone too bassy
Hi,  
I've got a Bassman 5F6A clone I've built some months ago. It's built in a head and I use it with a 4x10 cabinet loaded with Weber VST P10R's.  
I found that it has too much bass, it sounds a little boomy. I play a CS Strat through it with bass control set to 1-2. More than this and there's a lot of ot bass. Not to mention with a Les Paul...  
There are no differences on the circuit itself, apart from the adjustable bias control, similar to blackface models, the first stage bypass cap is 25 mfd, instead of the 250 mfd. The filter caps are Solens PP. I built originaly with 40-20-20-8, but I have decreased the first filter value to 33 mfd, to check if it has something to do with too much filtering, so it's now 33-20-20-8.  
I've read that when you use Solen PP caps in the filtering, you must decrease the corresponding electrolytic values, but I don't understand the technical reason for it.  
I use Sozo signal caps, carbon comp and carbon film resistors and a MM choke and OT.  
Any ideas of why it has excessive bass?  
Apart from it, it sounds incredible.  
thanks.
 
8/31/2005 3:11 AM
Chris/CMW amps
email

Hi Rene  
 
Altough in the middle of moving what's life without Ampage? :)  
 
Here are some suggestions:  
 
- did you use a 12aY7 as V1?  
 
- lower the couplingcaps from the PI to the outputtubes to something like 0.022  
 
- lower the V1 cathodebypasscap to 1u  
OR  
- split the 1st cathodes to >1k5/>0.47u each  
 
- use 40-50u at the 1st node (plates)  
 
- maybe up the value for the pre-amp-node to something like 16u  
 
- up the amount of neg.feedback by lowering the 27k resistor somewhat  
 
- use a 6k8 resistor in the PI tail  
 
It was originally a bassamp (hence the name, ha ha :D)...  
 
Hope this helps/let us know/I'll be back :)  
 
Chris
 
 
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8/31/2005 9:36 AM
Man o'Blues
I generally keep the bass on 0 or 1 on my 5F6-A clone, the Vicky clone and all the RI's I've played thru. I believe it's just the nature of the beast when you crank these amps up. At low volumes, however, it's nice to be able to dial in some more bass when you want it.
 
8/31/2005 11:33 AM
Shea
email

I use Solens caps as filters in my 5F8A twin clone, which is pretty much the same circuit in an 80 watt / 2x12 version, and I don't have that problem with excess bassiness. The filters are stock values, or the closest values that Solens stocks.  
 
Shea
 
9/1/2005 1:36 AM
Rene
Thank you for your answers.  
I use Solens as filter caps in my other homebuilt amps, and I like the way they sound.  
I played through a RI Bassman many years ago, and I didn't remember it to be so bassy, on the other hand I remember it was too bright. That's way I was surprised at first with my amp, as I didn't expect it due to the fact that the components values are the same as the RI Bassman.  
regards.
 
9/1/2005 3:11 AM
Dave H
email

I’d reduce the value of the 0.02u coupling cap between the first stage plate and volume control on one channel. Try 2n2 and adjust to taste from there. I’d also change the bass pot to 220k or 250k log. It will have a more gradual taper than the 1M pot. There’s not much increase in bass above 250k. Here’s my homebrew circuit with the mods.  
 
http://jaffa.members.beeb.net/scm/Northcourt50.pdf  
 
Dave
 
9/24/2005 7:38 PM
Gord
I built a 5F6A clone, and used the tone stack with a 100k slope resistor and .1uf bass cap. That cuts out a ton of bottom end. I have been tracking photos of original 5F6A Bassman amps on eBay for well over a year now, and have yet to see one wired like on the schematic. Every single original 1959 Bassman I've seen on eBay in the past year has been wired this way, without exception.  
 
Another change that might affect the tone of the amp is to use the 25k pot presence control with the extra 4700 Ohm resistor. All of the Bassman amps on eBay that I've seen were wired like this, too.  
 
Since were talking about it, all the amps I've seen on eBay had a 6800 Ohm resistor in the phase inverter as opposed to 10k.  
 
I'm convinced that that famous, elusive Bassman tone we're all after is the one in the amps, not on paper. It makes sense to me.  
 
You can try out these three mods, and if you don't like them, you can always go back to what you had. It doesn't hurt.  
 
I believe that there are a couple of vintage Bassmans on eBay right now, and they are wired just as I described above.  
 
When wired as above, I love the sound coming out of the amp's dark channel with the mid control set all the way up.  
 
Gord
 
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