Weird Heater Supply Problem - And other solutions!
Moderator: VelvetGeorge
- neikeel
- Senior Member
- Posts: 7231
- Joined: Tue Dec 06, 2005 8:31 am
- Location: Suffolk, England
Re: Weird Heater Supply Problem - And other solutions!
Yes, I agree
A lot of people leave those caps out, usually bedroom players.
A lot of people leave those caps out, usually bedroom players.
Neil
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
Ok, in an effort to figure out why my JCM800 2203 is very dark sounding even with 6L6 output tubes (which I have always associated with being bright and with extended low range), I am going to list the differences between the standard JCM800 2203 specs than what I have cooking in my amp.
The amp is loud, VERY loud. But it does not have the typical JCM800 bright, rip your head off cut that I am expecting as my baseline before hot-rodding it.
The only thing that I am leaning towards is the cheap Chinese Bugera output transformer, spec'd for a JCM900 clone, is not the right OT for a 2203. How much of a difference would this make?
- 6L6 Output Tubes
- 525vdc loaded B+
- Higher B+ in the preamp than spec'd due to different PT
- Non Center Tapped HV and Filament - Commensurate mods to make it work
- 1K 5 Watt screen grid resistors instead of 470 ohm 5 watt screen grids usually spec'd for a 6L6
- Bugera 1990 Power and Output Transformers - This is a JCM900 4100 knock off amp
The amp is loud, VERY loud. But it does not have the typical JCM800 bright, rip your head off cut that I am expecting as my baseline before hot-rodding it.
The only thing that I am leaning towards is the cheap Chinese Bugera output transformer, spec'd for a JCM900 clone, is not the right OT for a 2203. How much of a difference would this make?
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
How can an amp be JCM800 bright but dark at the same time?
The OT can make a difference but I doubt it would make that much of a difference. I personally think of the OT as fine tuning. I don't think it can make or break an amp, unless it's horrendously bad!
To lower the voltages in the preamp you should have two 10K droppers between the screen node and PI node. Can't remember if you've done this or not.
Leave the 1K screen grid resistors in as you're extending the life of the valves with this instead of 470Ohm. You won't notice any tonal difference with this anyway unless you run the master high and drive the hell out of the power amp. Even then 470Ohm vs 1K won't make much difference.
The bright cap you installed, you say it didn't make any difference, are you running the gain on 10? If so then you won't notice any difference at all.
The OT can make a difference but I doubt it would make that much of a difference. I personally think of the OT as fine tuning. I don't think it can make or break an amp, unless it's horrendously bad!
To lower the voltages in the preamp you should have two 10K droppers between the screen node and PI node. Can't remember if you've done this or not.
Leave the 1K screen grid resistors in as you're extending the life of the valves with this instead of 470Ohm. You won't notice any tonal difference with this anyway unless you run the master high and drive the hell out of the power amp. Even then 470Ohm vs 1K won't make much difference.
The bright cap you installed, you say it didn't make any difference, are you running the gain on 10? If so then you won't notice any difference at all.
- neikeel
- Senior Member
- Posts: 7231
- Joined: Tue Dec 06, 2005 8:31 am
- Location: Suffolk, England
Re: Weird Heater Supply Problem - And other solutions!
I am puzzled as none of the things that you have done would cause what you are hearing, unless the speaker cab is no good. Lowering preamp voltages will not brighten it up, but will help it break up earlier.
- it is probably the OT, assuming no wiring errors.
- it is probably the OT, assuming no wiring errors.
Neil
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
Actually we have overlooked one thing. What guitar is it? What pickups? And are you plugged straight into the amp? Also what settings are you using?
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
IMG_20171024_082854160 by Paul Abbott, on Flickr
IMG_20171024_082859010 by Paul Abbott, on Flickr
IMG_20171024_082909548 by Paul Abbott, on Flickr
Yes, this is a 6.8K on the V1A cathode instead of 10K
IMG_20171024_082914495 by Paul Abbott, on Flickr
IMG_20171024_082920300 by Paul Abbott, on Flickr
IMG_20171024_082925017 by Paul Abbott, on Flickr
IMG_20171024_082938075 by Paul Abbott, on Flickr
IMG_20171024_082929607 by Paul Abbott, on Flickr
IMG_20171024_082952595 by Paul Abbott, on Flickr
IMG_20171024_082957148 by Paul Abbott, on Flickr
IMG_20171024_083002699 by Paul Abbott, on Flickr
IMG_20171024_083016494 by Paul Abbott, on Flickr
IMG_20171024_083025921 by Paul Abbott, on Flickr
IMG_20171024_083034716 by Paul Abbott, on Flickr
IMG_20171024_083043852 by Paul Abbott, on Flickr
IMG_20171024_082859010 by Paul Abbott, on Flickr
IMG_20171024_082909548 by Paul Abbott, on Flickr
Yes, this is a 6.8K on the V1A cathode instead of 10K
IMG_20171024_082914495 by Paul Abbott, on Flickr
IMG_20171024_082920300 by Paul Abbott, on Flickr
IMG_20171024_082925017 by Paul Abbott, on Flickr
IMG_20171024_082938075 by Paul Abbott, on Flickr
IMG_20171024_082929607 by Paul Abbott, on Flickr
IMG_20171024_082952595 by Paul Abbott, on Flickr
IMG_20171024_082957148 by Paul Abbott, on Flickr
IMG_20171024_083002699 by Paul Abbott, on Flickr
IMG_20171024_083016494 by Paul Abbott, on Flickr
IMG_20171024_083025921 by Paul Abbott, on Flickr
IMG_20171024_083034716 by Paul Abbott, on Flickr
IMG_20171024_083043852 by Paul Abbott, on Flickr
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
Ok, the other details.
I am using a 1x12 Jet City cab with a Eminence Wizard in it at 8 Ohms. I have also used a JCM800 1960a with Veteran 30s in it also at 8 Ohms.
The guitar is a maple necked strat with a Dimarzio Super Distortion in the bridge. Also used an Axis 20 with stock pickups in it.
No effects. Straight in. Treble at 10, presence at 10, Mids at 5 and bass at 5. All of the tone stack works great. Its just not cutting like I remember 2203/4s being. I had an 1982 2204 with EL34s in it that had plate voltages at 390vdc.
I am using a 1x12 Jet City cab with a Eminence Wizard in it at 8 Ohms. I have also used a JCM800 1960a with Veteran 30s in it also at 8 Ohms.
The guitar is a maple necked strat with a Dimarzio Super Distortion in the bridge. Also used an Axis 20 with stock pickups in it.
No effects. Straight in. Treble at 10, presence at 10, Mids at 5 and bass at 5. All of the tone stack works great. Its just not cutting like I remember 2203/4s being. I had an 1982 2204 with EL34s in it that had plate voltages at 390vdc.
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
Not sure if I'm looking at it right but it looks like there isn't a 4.7K resistor bypassing the presence pot to ground? Without that the negative feedback circuit won't work correctly which would explain it.
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
I took it out on purpose. It was causing scratchiness. The pot does work and so does the negative feedback.Littlewyan wrote: ↑Tue Oct 24, 2017 4:48 pmNot sure if I'm looking at it right but it looks like there isn't a 4.7K resistor bypassing the presence pot to ground? Without that the negative feedback circuit won't work correctly which would explain it.
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
Ok that doesn't sound right. The pot will work but it's only grounded through the 0.1uF capacitor at the moment. So essentially the feedback network is only working on frequencies that can go through that capacitor, which would explain why the amp sounds so dark.
On the other hand it definitely shouldn't be scratchy with the resistor!
On the other hand it definitely shouldn't be scratchy with the resistor!
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
Ok, I will give that part of the circuit another once over. I may try the 5K pot instead of the 25K with the resistor and all that stuff.
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
To be honest if you don't mind the scratchiness the 5K Pot circuit (on the older amps) has a much better range. HOWEVER, you might find it too bright set at midway. Simply because the 25K Pot with the extra resistor doesn't actually do much until you turn it past 5. Hope that makes sense.
Personally I prefer the older circuit but I have the newer one in my Master Volume Amp.
Personally I prefer the older circuit but I have the newer one in my Master Volume Amp.
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
I didn't care about the scratchiness either, but it didn't sound right with the resistor installed anyway. So I simply removed it. I will go back to it and try again. Ha!Littlewyan wrote: ↑Tue Oct 24, 2017 5:23 pmTo be honest if you don't mind the scratchiness the 5K Pot circuit (on the older amps) has a much better range. HOWEVER, you might find it too bright set at midway. Simply because the 25K Pot with the extra resistor doesn't actually do much until you turn it past 5. Hope that makes sense.
Personally I prefer the older circuit but I have the newer one in my Master Volume Amp.
-
- Senior Member
- Posts: 200
- Joined: Fri Dec 06, 2013 9:27 am
- Just the numbers in order: 13492
- Location: United Kingdom
Re: Weird Heater Supply Problem - And other solutions!
Yeah give it a go mate. Let us know
-
- Senior Member
- Posts: 169
- Joined: Wed Jun 10, 2015 1:58 pm
- Just the numbers in order: 13492
- Location: Oceanslime, CA
Re: Weird Heater Supply Problem - And other solutions!
Gave it a go I did. Didn't make a difference.
So I then went all experimental on the amp and decided to swap capacitors around in order to brighten up the amp. It ended with me taking a .0022 cap for the phase inverter capacitor and it did brighten the amp up slightly. But it is still muffled sounding and congested.
I am 99% sure the output transformer is a severe bottleneck or something. I unsoldered the OT from the amp and measured primary resistance of 30 ohms.
Does that sound right?
So I then went all experimental on the amp and decided to swap capacitors around in order to brighten up the amp. It ended with me taking a .0022 cap for the phase inverter capacitor and it did brighten the amp up slightly. But it is still muffled sounding and congested.
I am 99% sure the output transformer is a severe bottleneck or something. I unsoldered the OT from the amp and measured primary resistance of 30 ohms.
Does that sound right?