Tightening up low end ?

william vogel

Well-Known Member
Joined
Dec 18, 2016
Messages
973
Reaction score
1,167
Oh I see. I have a 500KL pot laying around so Ill try and sub that in for the 1meg.

For now, I have settled with the NFB at 16 ohms and the 33k resistor, it sounds much tighter. Do you suggest I get a 50+50 cap to replace the 32+32 to get a more tight low end?
I don’t know where you set the bass knob but most of us usually run it nearly on 0 maybe 1. If this is the case, you can swap in a 100k and still have plenty of adjustment. 0 on the 1Meg pot is theoretically 0 ohms. It’s used as a variable resistor vs a potentiometer so the fact that it is 0-1000000 ohms just means you get little to no adjustment range if 2 is the most you use. A much lower resistance would give you a better range of adjustment until you hit 0.
 

junk notes

Well-Known Member
Joined
Dec 10, 2018
Messages
4,014
Reaction score
5,516
make the 68' lead sound more like a super lead
Your amp should have a .0022 V1B cap on the circuit board.
increased filtering
With 50s on the screens you will feel the difference coming from the 32s..

With your amp, it is not unusual to have 32s (early) and (later) 50s in the same year, but IIRC the metal face and following year(s) started using 50s all around.

Keep us posted after you install the new screens. What e-cap is on the board, 32μF+32μF as on the Ceriatone schematic?
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
Your amp should have a .0022 V1B cap on the circuit board.
yep I have a 0.0022 v1b cap installed.

With your amp, it is not unusual to have 32s (early) and (later) 50s in the same year, but IIRC the metal face and following year(s) started using 50s all around.

Keep us posted after you install the new screens. What e-cap is on the board, 32μF+32μF as on the Ceriatone schematic?
Yeah this is a 68’ clone which had 32uf all round, the cap on the board is 32+32. From what I’ve searched I’m unable to find a dual section axial cap more than 33+33, I think that’s why they switched to a chassis mounted cap in the later models for a higher capacitance.
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
I don’t know where you set the bass knob but most of us usually run it nearly on 0 maybe 1. If this is the case, you can swap in a 100k and still have plenty of adjustment. 0 on the 1Meg pot is theoretically 0 ohms. It’s used as a variable resistor vs a potentiometer so the fact that it is 0-1000000 ohms just means you get little to no adjustment range if 2 is the most you use. A much lower resistance would give you a better range of adjustment until you hit 0.
I set it at about 3-4, I find that’s a good balance, anything more and it’s just too loose. With the 0.022 v1b cab it’s even worse hence why I switched to the 0.0022
 

william vogel

Well-Known Member
Joined
Dec 18, 2016
Messages
973
Reaction score
1,167
I set it at about 3-4, I find that’s a good balance, anything more and it’s just too loose. With the 0.022 v1b cab it’s even worse hence why I switched to the 0.0022
Changing the bass pots value to 500k is only going to require you to increase the setting from 3-4 to a higher level only to achieve the same bass effectiveness. Because the bass control is wired as a variable resistor, whatever resistance is at 3-4 on the 1Meg pot will not be sufficient at 3-4 with a 500k pot. If it were wired as a potentiometer, the change would have an effect.
 

Pete Farrington

Well-Known Member
Joined
Jan 18, 2021
Messages
1,443
Reaction score
1,591
Location
Staffordshire UK
For the settings I use, I find that a 1M log control doesn’t have good resolution.
Yes it can be set anywhere from 0-1M, but in reality, getting it right can be something of a hair trigger, flipping from ‘not quite enough’ to ‘a bit too much’ too easily.

If someone is using a boomy cab and having to turn it down to 0, in some scenarios they may wish more bass cut was available. A useful mod then is to wire the mid control like that of a Fender black panel Twin Reverb etc, ie link the wiper and hot terminals together.
 
Last edited:

neikeel

Well-Known Member
Joined
Feb 12, 2014
Messages
7,192
Reaction score
6,732
A 68 would have 50+50 mains, 50 PI and 50 screens, 32/32 preamp anyway
I like 27k/16 NFB on a tweaked 100
330uF V1A is technically too big
George Metro used to lower the value of the coupler into the PI (0.022) using a cap box then measure the sweep response to get what he wanted (measured from originals)
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
A 68 would have 50+50 mains, 50 PI and 50 screens, 32/32 preamp anyway
I like 27k/16 NFB on a tweaked 100
330uF V1A is technically too big
George Metro used to lower the value of the coupler into the PI (0.022) using a cap box then measure the sweep response to get what he wanted (measured from originals)
IIRC a 68' had 40+40 on mains and screens and 32+32 for pre amp.

If im only using the bright channel, would the v1a bypass cap affect my tone?
 

william vogel

Well-Known Member
Joined
Dec 18, 2016
Messages
973
Reaction score
1,167
The early Marshall’s would have some mixed values for filter capacitors because they used what was available. The difference in 80uF and 100uF filtering can be felt but it’s not night and day difference. What you’re looking to do might need to be at least double (200uF). Have you considered using 6v6 tubes like maybe JJ instead of EL34’s. I don’t know if you can accept the power loss (25 watts) but reducing the power with 6v6 will lower the current demand from the power transformer and give it less ripple and more stable voltage output.
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
The early Marshall’s would have some mixed values for filter capacitors because they used what was available. The difference in 80uF and 100uF filtering can be felt but it’s not night and day difference. What you’re looking to do might need to be at least double (200uF). Have you considered using 6v6 tubes like maybe JJ instead of EL34’s. I don’t know if you can accept the power loss (25 watts) but reducing the power with 6v6 will lower the current demand from the power transformer and give it less ripple and more stable voltage output.
I see, I already have a 6v6 amp, I prefer the sound of el34s, plus I don’t think the 6v6 can handle the voltages that are supplied by this amp if I’m not wrong.

I’ll see how the 50uF caps affect the low end.
 

junk notes

Well-Known Member
Joined
Dec 10, 2018
Messages
4,014
Reaction score
5,516
What cab and speakers? Is your cab on the floor or does it have casters?
 

william vogel

Well-Known Member
Joined
Dec 18, 2016
Messages
973
Reaction score
1,167
I see, I already have a 6v6 amp, I prefer the sound of el34s, plus I don’t think the 6v6 can handle the voltages that are supplied by this amp if I’m not wrong.

I’ll see how the 50uF caps affect the low end.
JJ’s can run at 450+ and Fender used to run them at about 440 in a Deluxe Reverb. I get that you like EL34’s though. I’m the same way.
 

Dblgun

Well-Known Member
Joined
Jan 6, 2019
Messages
491
Reaction score
897
Location
AZ
Yeah this is a 68’ clone which had 32uf all round, the cap on the board is 32+32. From what I’ve searched I’m unable to find a dual section axial cap more than 33+33, I think that’s why they switched to a chassis mounted cap in the later models for a higher capacitance.
I don't know that you would need or have any interest but if you're looking for dual 50uf's this where I have gotten them.
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
I don't know that you would need or have any interest but if you're looking for dual 50uf's this where I have gotten them.
Thank you! I think that’s the exact one ceriatone uses for their 70s + spec amps. I probably don’t need 50+50 for the pre amp yet, I’ll see how the dual 50s on the mains and screens affect it first.
 

playloud

Well-Known Member
Joined
Dec 28, 2020
Messages
790
Reaction score
938
Update: Just received and installed the new 50+50 caps, the amp sound much more punchy and tight. I would call this a success! Much more kerrang which I dig.

Even replacing the 50+50uf preamp can in my Super Bass with a 32+32uf made a pretty noticeable difference (for the worse, in my opinion).

I'm surprised swapping out filter cap values isn't discussed more often as a completely-reversible "mod". It's cheaper than tube rolling, that's for sure.
 

sdn25

Active Member
Joined
Apr 24, 2022
Messages
260
Reaction score
159
probably because folks do enough damage just replacing resistors and coupling/bypass capacitors?
Definitely but replacing filter caps for tone changes should be talked about, like playloud said its much cheaper and can be very effective.
 


Top