Is 400 VDC B+ too low for a 2204 to sound heavy and punchy?

[FourT6and2]

Might you be conflating a lower HT with one that’s more saggy?

Nope.

I don’t think that’s necessarily the case, (though it might be with the particular PTs here ).
For a given OT load and reservoir and screen grid cap values, as with Marshalls, and for a given HT winding gauge wire, the lower HT should be stiffer.

Nope. Higher B+ = higher preamp voltages = stiffer, brighter, less gain. If you compensate by raising B+ dropper values to keep preamp voltages the same, that's another story. It's the reason why some people use a variac or raise the value of V1 plate resistors to lower plate voltage. That gives you more grit, gain, and a looser feel = "brown sound." And it's the reason some builders, like Cameron, typically shoot for well over 500v B+ to get a more angry, aggressive, tight sound.

 

[2L man]

Knowing operative voltages without knowing output transformer impedance does not answer much!

Drawing loadlines is good practice to compare circuits.

 

[shredless]

Is that measured at idle, or with the amp putting out audio power?

Hmmm...idle....? of course l dont know the intracacies of those two choices.
I added resistors to b+ dropper, the big 10k on the right...and my b+ reads 385 when amp is on and no signal.
Idle?
I found a old jmp schematic showing voltages and added resistors till l arrived there.

Im a hack with some happy accidents

 

[LPman]

Nope.



Nope. Higher B+ = higher preamp voltages = stiffer, brighter, less gain. If you compensate by raising B+ dropper values to keep preamp voltages the same, that's another story. It's the reason why some people use a variac or raise the value of V1 plate resistors to lower plate voltage. That gives you more grit, gain, and a looser feel = "brown sound." And it's the reason some builders, like Cameron, typically shoot for well over 500v B+ to get a more angry, aggressive, tight sound.

Does that mean that if I remove one of the two 10k dropping resistors and raise preamp voltage (which I did) I arrive at the same tonal ballpark (tightness, punchiness) as if I had a higher plate voltage Power Transformer to begin with?

 

[FourT6and2]

Does that mean that if I remove one of the two 10k dropping resistors and raise preamp voltage (which I did) I arrive at the same tonal ballpark (tightness, punchiness) as if I had a higher plate voltage Power Transformer to begin with?

Yes and no. Lowering your main B+ dropper value will raise your preamp voltages. But your power section will stay the same. Replacing PT with one that has higher secondaries will increase everything—both preamp voltages AND power section voltages (screens, plate voltage, bias section, etc.).

 

[LPman]

Yes and no. Lowering your main B+ dropper value will raise your preamp voltages. But your power section will stay the same. Replacing PT with one that has higher secondaries will increase everything—both preamp voltages AND power section voltages (screens, plate voltage, bias section, etc.).

What does it mean in terms of tonal response? By power section staying the same, does it mean that I get a punchier tone at only lower volumes with the raised preamp voltage but at cranked levels it wouldn't do much?

Which way would I get a punchier tone at high volumes: with 400 VDC plate voltage and one of the 10k droppers snipped or with 450 VDC but both droppers in place?

 

[LPman]

What does it mean in terms of tonal response? By power section staying the same, does it mean that I get a punchier tone at only lower volumes with the raised preamp voltage but at cranked levels it wouldn't do much?

Which way would I get a punchier tone at high volumes: with 400 VDC plate voltage and one of the 10k droppers snipped or with 450 VDC but both droppers in place?

(double post - please remove)

 

[2L man]

Do you like the sound of High input more? Is "punch" tight lows to you?

While pre amp voltages can have effect to sound I think it is small. Tuning stage gains might produce some gains but adding one more pre amp tube might be needed?

Have you test how you like sound without power stage NFB? There might come 3db?

Perhaps just higher bias current is needed? If you test ihigher bias watch that tubes do not redplate too much when you play full power!

Often Variac adjust output higher than the Mains voltage is and if you could use Variac it is fast method to test how higher voltatages effect to sound. I like "brown sound" which might be opposite for your "punch"? Brown sound comes when voltages are dropped.

 

[LPman]

Do you like the sound of High input more? Is "punch" tight lows to you?

While pre amp voltages can have effect to sound I think it is small. Tuning stage gains might produce some gains but adding one more pre amp tube might be needed?

Have you test how you like sound without power stage NFB? There might come 3db?

Perhaps just higher bias current is needed? If you test ihigher bias watch that tubes do not redplate too much when you play full power!

Often Variac adjust output higher than the Mains voltage is and if you could use Variac it is fast method to test how higher voltatages effect to sound. I like "brown sound" which might be opposite for your "punch"? Brown sound comes when voltages are dropped.

By punchiness I mean a big tight bold low-end that is ideal for firm and fast palm-muting, a low-end that kicks you in the chest. So it's kinda the opposite of brown sound. That's why I like my bias on the lower side around 60%. I don't need and don't like high-gain, just cranked Plexi / 2204 territory but the lows must be percussive, fast and punchy. That jackhammer sound.

 

[2L man]

If Screen resistors are 1.5k you could test 1k because screen voltage has very high effect to pentode power tube gain. When bias is only 60% this should not overheat tubes.

Changing B+1 electrolyte to type which can release higher current should help. On datasheet the value to watch is internal resistance and the lower the m Ohm value the higher the peak current it can deliver. When you search it compare same capacitance electrolyts because capacitance has almost direct effect. Or installing polycapacitor parallel with electrolyt might improve punch because it can deliver high current peaks.

Eventually the power transformer can become limiter because it must deliver the current without too high voltage drop.

 

[LPman]

If Screen resistors are 1.5k you could test 1k because screen voltage has very high effect to pentode power tube gain. When bias is only 60% this should not overheat tubes.

Changing B+1 electrolyte to type which can release higher current should help. On datasheet the value to watch is internal resistance and the lower the m Ohm value the higher the peak current it can deliver. When you search it compare same capacitance electrolyts because capacitance has almost direct effect. Or installing polycapacitor parallel with electrolyt might improve punch because it can deliver high current peaks.

Eventually the power transformer can become limiter because it must deliver the current without too high voltage drop.

Thanks for the great suggestions, I will look into that.

But my basic question still stands. What is the difference between raising the preamp voltage by snipping a dropping resistor (or even reducing the value of the remaining one) vs having a higher plate voltage to begin with but with less stock preamp voltage? Can I reach the same tightness by incresing the preamp voltage or is that only beneficial at lower volumes?

400 VDC with one 8.2K dropping resistor vs 450 VDC with two stock 10K dropping resistors. Which will be tighter at high volumes?

I had a '78 2204 that had a replaced Dagnall PT with 450 VDC. I compared it to my '69 a lot. They had the exact same tonal DNA but the 2204 was tighter and harsher. I liked its super fast-responding bottom-end better (not a night and day difference though) but the lead tones were ear-piercing compared to my '69 JMP.

 

[FourT6and2]

Thanks for the great suggestions, I will look into that.

But my basic question still stands. What is the difference between raising the preamp voltage by snipping a dropping resistor (or even reducing the value of the remaining one) vs having a higher plate voltage to begin with but with less stock preamp voltage? Can I reach the same tightness by incresing the preamp voltage or is that only beneficial at lower volumes?

400 VDC with one 8.2K dropping resistor vs 450 VDC with two stock 10K dropping resistors. Which will be tighter at high volumes?

I had a '78 2204 that had a replaced Dagnall PT with 450 VDC. I compared it to my '69 a lot. They had the exact same tonal DNA but the 2204 was tighter and harsher. I liked its super fast-responding bottom-end better (not a night and day difference though) but the lead tones were ear-piercing compared to my '69 JMP.

That's a hard question to answer. But your comparison with those two amps seems accurate. Without changing anything else in the circuit, you're gonna get a tighter response, but it will be a bit more harsh—which you experienced with those two amps. That can be addressed though.

It's typically better to start with more voltage because you can always reduce it. But you can't increase it. If a PT yields 400 volts, that's it. You can't increase it. You can only help reduce it less as you get farther and farther down the B+ rail by reducing/removing dropping resistors and/or their values. But the power section will still see the same voltage. So for example, if your amp has 400v on the power tube plates, and you reduce your main B+ dropper from 18K to 10K, you will increase your preamp voltages, which will tighten things up and give you a cleaner, punchier sound at the expense of reducing some hair (brown sound) and making the preamp a little brighter.

Nothing exists on its own. When you mod an amp you have to also think about what other things need to be changed to achieve your desired results. So if the amp gets brighter and loses some hair/edge, you need to also adjust other things.

All in all, a stock 2203 or 2204 doesn't have a super fast attack and super tight, thundering low end in their stock form. So if you want that kind of thing, a bunch of other mods need to be done beyond just altering the voltages.

 

[LPman]

That's a hard question to answer. But your comparison with those two amps seems accurate. Without changing anything else in the circuit, you're gonna get a tighter response, but it will be a bit more harsh—which you experienced with those two amps. That can be addressed though.

It's typically better to start with more voltage because you can always reduce it. But you can't increase it. If a PT yields 400 volts, that's it. You can't increase it. You can only help reduce it less as you get farther and farther down the B+ rail by reducing/removing dropping resistors and/or their values. But the power section will still see the same voltage. So for example, if your amp has 400v on the power tube plates, and you reduce your main B+ dropper from 18K to 10K, you will increase your preamp voltages, which will tighten things up and give you a cleaner, punchier sound at the expense of reducing some hair (brown sound) and making the preamp a little brighter.

Nothing exists on its own. When you mod an amp you have to also think about what other things need to be changed to achieve your desired results. So if the amp gets brighter and loses some hair/edge, you need to also adjust other things.

All in all, a stock 2203 or 2204 doesn't have a super fast attack and super tight, thundering low end in their stock form. So if you want that kind of thing, a bunch of other mods need to be done beyond just altering the voltages.

Thank you for explaining in more details. So if I understand it correctly, I can manipulate the amp to have the feel and response of a higher plate voltage version of a JMP by reducing the dropping resistors thus significantly raising preamp voltages. Does this modification make the amp's response tighter at cranked levels too where the power section dominates the tone or only at lower levels before the power tube saturation 'kicks in' audibly?

/ BTW, I'm happy with the tightness and attack of a stock 2204, for a basic vintage circuit that is not high gain at all I find it exceptional (and I only turn up the gain knob to 6.5 at max because above that the amp loses it's overall clarity). I wouldn't mod a 2204 for that thundering low-end, I'd rather buy a JVM205 as a 2nd amp instead which does just like that (I'm just freshly back from comparing my amp to a friend's JVM and it got the exact same tone on the cranked orange channel with the gain at about 2.5 as mine with the gain at 6.5. Then with the gain at 5 on the JVM, it transformed into an insane super-charged 2204! I loved it and was flabbergasted how similar they sounded at the core tonal DNA level). /

 

[FourT6and2]

Thank you for explaining in more details. So if I understand it correctly, I can manipulate the amp to have the feel and response of a higher plate voltage version of a JMP by reducing the dropping resistors thus significantly raising preamp voltages. Does this modification make the amp's response tighter at cranked levels too where the power section dominates the tone or only at lower levels before the power tube saturation 'kicks in' audibly?

/ BTW, I'm happy with the tightness and attack of a stock 2204, for a basic vintage circuit that is not high gain at all I find it exceptional (and I only turn up the gain knob to 6.5 at max because above that the amp loses it's overall clarity). I wouldn't mod a 2204 for that thundering low-end, I'd rather buy a JVM205 as a 2nd amp instead which does just like that (I'm just freshly back from comparing my amp to a friend's JVM and it got the exact same tone on the cranked orange channel with the gain at about 2.5 as mine with the gain at 6.5. Then with the gain at 5 on the JVM, it transformed into an insane super-charged 2204! I loved it and was flabbergasted how similar they sounded at the core tonal DNA level). /

The amp should be a bit tighter/stiffer with higher preamp voltages. But it might not be exactly what you're looking for. Or it might be. Only one way to know for sure. It's a simple mod. One resistor, so give it a shot.

 

[Pete Farrington]

If higher preamp HT node voltage is the goal, consider feeding them from the screen grid node, rather than the LTP node.
eg similar to an AC30 etc https://el34world.com/charts/Schematics/files/Vox/Vox_ac30cc2_ac30cc2x_2005_sm.pdf

 

[neikeel]

My personal experience is that if you want clarity and more headroom (but is that really punch?/) at real world operating volumes there is a sweet spot where your preamp voltages sit, where that sits for you will be trial and error. If you sit with your master on 8-10 you will get very different responses with Preamp gain in same region.
@2L man we are talking about a 2204 which by definition will be a Drake 784-139 which has a primary of 3k4.

Also if someone is reading this and thinks that all the references to 'snipping' the dropping resistor - don't as you will lose all of your down stream preamp voltages.
To experiment just use a croc 'frig lead' to bypass one of the 8k2 or 10k droppers in series between bias circuit and NFB resistor on your board. You can really experiment by crocking another resistor in parallel with one for 'in between' voltages.

 

[2L man]

My personal experience is that if you want clarity and more headroom (but is that really punch?/) at real world operating volumes there is a sweet spot where your preamp voltages sit, where that sits for you will be trial and error. If you sit with your master on 8-10 you will get very different responses with Preamp gain in same region.
@2L man we are talking about a 2204 which by definition will be a Drake 784-139 which has a primary of 3k4.

Also if someone is reading this and thinks that all the references to 'snipping' the dropping resistor - don't as you will lose all of your down stream preamp voltages.
To experiment just use a croc 'frig lead' to bypass one of the 8k2 or 10k droppers in series between bias circuit and NFB resistor on your board. You can really experiment by crocking another resistor in parallel with one for 'in between' voltages.

3k4 OT and 400V is already considerable load for the tubes

Loadline peaks come about 45W each tube but when they alternate that is still OK.

It is very easy to short voltage dropper resistors tack soldering a piece of wire to their legs. I think their other or function is to lessen interaction between amp stages and when bypassed cause perhaps oscillation symptoms?

There are schematics which pre amp stage feeds are parallel (not typical chained) from power supply having dropper resistors and then voltages come higher.

 

[AndyD]

This is a very interesting discussion and ties in with some experimenting I have been doing with a recent “Neil Special “ ( 1987/2204 switchable) build. The PT I used gives a B+ of approximately 475v. I initially had 100k on the 4 ohm tap for the NFB and had 18k > 10k > 10k dropping string. This meant I had about 230v pin1 and 260v pin 6 on V1 which instinctively seemed a bit high to me. Output valves were biased at 60% and 65% respectively. The result was very pleasing. On the 2204 setting, the amp was loud, punchy and clear with sweetness to the note. Reminded me very much of the Jimmy Page Maddison Square Garden sound. Definitely more headroom and overall sounding more like a 100watter than a 50w amp. I recently tried increasing the first dropper to 20k and lowered the NFB to 47k /8ohm and as a result lost that sound. I think the relationship between the preamp and output voltages plus the influence of the NFB (probably the biggest influence in this case) are key. Higher plate voltage in general gives more headroom and a tighter response. The opposite is true also which is why big amps have big sound!

 

[LPman]

It's certainly interesting. I've always been told that it's the OT to look out for to be original when buying an amp because that's the one with the biggest effect on tone. Turns out that it's not exactly the case.

I have my 2204 circuit '69 JMP's one 10K dropping resistor jumpered, the voltage selector set to 220/230 V (I'm in the EU) and the bias on the colder side. This way I was able to reach a plate voltage of 400-410 VDC from my '74 PT in it. I started with 360 VDC (with the selector on 240/250 V and a fairly hot bias), so it's not too bad. The amp is definitely much tighter and aggressive than either my '89 Jubilee was or my 2205 or any other high wattage amp I've had before (Laneys, Oranges) except a '78 2204 with a replaced Dagnall PT that had 450 VDC.

That amp definitely had a tighter and faster-responding tone. I decided to keep the current '69 one because I found it to be more musical and thicker sounding overall. I keep having an itch though for that super tight and super fast sound more and more.