Marshall 2061 - Ceriatone Layout Redplate Help

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l4ent
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Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

Can someone help me with next steps here?

bought this "amazing build" but it was redplating

So i'm reading that this is a common issue with this model? Crazy voltages and redplating, now slightttt (have to go to a dark room) but still there. The transformer should be spec'd correctly based on the layout showing the 290 for primary, i'm getting like 300 there , so not really sure why everything is so high. Model used here is PT -290-50 HT-6179-50

So far i've upped the sag resistor from 22 ohm to 34 ohm, the bias resistor is now at 165 ohms

DCV Pins with Tubes giving the same readings
1 N/A
2 V1 - 26mv, v2 33mv
3 14.18V
4 .2mv
5 0
6 N/A
7 375v
8 N/A
9 382v

If i go up to like 210 ohms for the bias resistor, will that kill the plate voltages?

whats next steps here?

love the sound of the circuit, seems like im close here but worried about upping the b+?

maybe add screen resistors?
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

As you can see on your bias calculator screenshot, the maximum for EL84s is 12W, and you're at nearly 15W.

Your cathode voltage is too high, and you need to adjust the cathode resistor value to bias them closer to where they should be. Your 20W amp is pushing 30W, that's dangerous.

Also, your plates are lower than your screen voltages. That's no good. Pin 9 should show a lower voltage than pin 7. I would add a 1K 3W resistor going to pin 9 and see where that puts you.

Most transformers rated at 290 will go to around 300 with modern electricity typically around 120V instead of 110 or 115 depending on what the transformer is expecting.

Pins 4 and 5 are your heaters on the power tubes, and you would use ACV to test them.

Thanks,
Josh
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by crgfrench »

That PT is a good one for this, its the Heyboer 6197.
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by zaphod_phil »

The screen grids control the behaviour of pentodes and tetrodes. The screen voltages first need to be reduced here, to return everything to normal operation.
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by geoff 1965 »

the 20 watters do push the el84's and i think that will give the amp it's certain character,your screen voltage needs to be addressed as mentioned earlier but actually your plate voltage is the same as this one from the downloads! have a look and check off your voltages on the tubes and B+ rail in comparison,good luck.
20W_Lead_2022.gif
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

so i was thinking of zeners to drop the b+ down about 20-30v, or upping the sag resister to 220 ohm, but i hear u the voltages are the same as this schematic minus the screens, can anyone answer the "why" and "how to resolve" without changing the tone too much, just don't want to redplate, seems im 20% over 100% :/
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

l4ent wrote:
Wed 05/20/20 1:19 pm
so i was thinking of zeners to drop the b+ down about 20-30v, or upping the sag resister to 220 ohm, but i hear u the voltages are the same as this schematic minus the screens, can anyone answer the "why" and "how to resolve" without changing the tone too much, just don't want to redplate, seems im 20% over 100% :/
What is your B+ reading?

What is your current cathode resistor value?

Add a 1K 3W resistor to the voltage feeding pin 9 of the power tubes. Or better yet, separate them, and add a 1K 3W resistor to Pin 9 of each tube connected to the voltage source they previously shared. Then recheck the voltages.

Thanks,
Josh
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

JMPGuitars wrote:
Wed 05/20/20 2:07 pm
l4ent wrote:
Wed 05/20/20 1:19 pm
so i was thinking of zeners to drop the b+ down about 20-30v, or upping the sag resister to 220 ohm, but i hear u the voltages are the same as this schematic minus the screens, can anyone answer the "why" and "how to resolve" without changing the tone too much, just don't want to redplate, seems im 20% over 100% :/
What is your B+ reading?

What is your current cathode resistor value?

Add a 1K 3W resistor to the voltage feeding pin 9 of the power tubes. Or better yet, separate them, and add a 1K 3W resistor to Pin 9 of each tube connected to the voltage source they previously shared. Then recheck the voltages.

Thanks,
Josh
Isn’t my b+ pin 7, 375v?
165 ohms for cathode resistor.

I will retake those measurements if I make mods I just want to be sure I’m making the “right” ones while staying true to the design.

I will consider adding screen resistors but as I understand it will affect the tone. I unserstand that pin 9 should be lower than 7 so this is a way to do it but looking at the schematic those voltages are actually about equal. I’m trying to understand why if everything is specd exactly to the layout why these mods are necessary or If something is off. As the transformer is specd the same and the parts used match the layout and schematics found on the net.

I could use the zener diodes on the center tap to drop b+ Which would be a fun little thing but according to the charts the high b+ isn’t a problem, should I do this?

it’s that the screen is higher which is causing to redplate. But the og does not have screen resistors and buying the 2061 or ceriatone or other clone will not have screen resistors. I understand how adding them will help but concerned about tone as this circuit just sounds so good and they manage to run without em. Do I need to add them?

I also understand I can increase the sag resistor to 220 and go up from there to drop the b+ To better levels and create more sag / get a rectifier tube which could be fun to add there cause I think there’s space but then og does not have this, do I need to increase sag resistor? This will affect tone surely from the specd 22/30ohm.

Also increasing the bias resistor to maybe 220 should get it closer to where I need to be but concerned about rising b+. I’m thinking this is the next step?

I’m also thinking that based on these responses, just dropping the screen voltage by adding these resistors (while yes changing tone a bit) will fix the red plate? Is that the simple solution to start?

I’m not sure where to start here.

If someone could answer those or help me understand further what the real “next step” is that would be great.

I see these “solutions” but it strikes me odd it needs to be so different from all of these specs I’m seeing. Shouldn’t it be achievable while being close to the product sold by these companies? Also since there seem to be many options I want to know the best route to take while maintaining this awesome sound I’m hearing
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

l4ent wrote:
Wed 05/20/20 3:19 pm
Isn’t my b+ pin 7, 375v?
No, that's your plate voltage, which is correct.

According to the schematic posted above, the B+ is supposed to be 385V, then drops to 370V after the first filter caps. B+ is the rectified voltage going to the filter caps.
l4ent wrote:
Wed 05/20/20 3:19 pm
I will consider adding screen resistors but as I understand it will affect the tone. I unserstand that pin 9 should be lower than 7 so this is a way to do it but looking at the schematic those voltages are actually about equal. I’m trying to understand why if everything is specd exactly to the layout why these mods are necessary or If something is off. As the transformer is specd the same and the parts used match the layout and schematics found on the net.
375 and 370 are not the same. The rule for pentodes is that the screen voltage should be lower than the plate voltage. If you want the correct tone for the amp, you must lower the screen voltage. The screen resistors also add a layer of protection.

Often these small changes in voltages are due to the tubes themselves. Other times it's a silly thing like forgetting to include screen resistors in a schematic.
l4ent wrote:
Wed 05/20/20 3:19 pm
I could use the zener diodes on the center tap to drop b+ Which would be a fun little thing but according to the charts the high b+ isn’t a problem, should I do this?

it’s that the screen is higher which is causing to redplate. But the og does not have screen resistors and buying the 2061 or ceriatone or other clone will not have screen resistors. I understand how adding them will help but concerned about tone as this circuit just sounds so good and they manage to run without em. Do I need to add them?
Your B+ is still unknown to us, so I don't know if you need to drop it. Your plate voltages are good right now.

If you're trying to capture the "OG" tone, then you need to pay attention to your voltages, not what clone amps have or don't have.
l4ent wrote:
Wed 05/20/20 3:19 pm
I also understand I can increase the sag resistor to 220 and go up from there to drop the b+ To better levels and create more sag / get a rectifier tube which could be fun to add there cause I think there’s space but then og does not have this, do I need to increase sag resistor? This will affect tone surely from the specd 22/30ohm.

Also increasing the bias resistor to maybe 220 should get it closer to where I need to be but concerned about rising b+. I’m thinking this is the next step?
No, this is backwards. Raising the resistor value will raise the voltage. You need to reduce the resistor value to drop the voltage. Try 150R or 130R. Measure your B+ before and after.
l4ent wrote:
Wed 05/20/20 3:19 pm
I’m also thinking that based on these responses, just dropping the screen voltage by adding these resistors (while yes changing tone a bit) will fix the red plate? Is that the simple solution to start?

I’m not sure where to start here.

If someone could answer those or help me understand further what the real “next step” is that would be great.

I see these “solutions” but it strikes me odd it needs to be so different from all of these specs I’m seeing. Shouldn’t it be achievable while being close to the product sold by these companies? Also since there seem to be many options I want to know the best route to take while maintaining this awesome sound I’m hearing
Steps as I've stated above:
1. Take your voltages, including your correct B+.
2. Adjust your cathode resistor to get to a better bias point.
3. Add 1K 3W screen resistors.
3. Take all your voltages again and share them here. Compare them to the schematic voltages.

Changing the screen voltages to the correct voltage is the right thing to do. I don't know that you would be able to perceive a tonal change. In any case, the correct voltage is generally the way it's supposed to sound.

The only specs that matter are the schematic. Making those changes will get you closer to those specs. That's what you want, and should give you the ideal tone, if you're trying to match the original. What people sell is an entirely different discussion, and doesn't fix your amp. A lot of people sell a lot of silly things for silly reasons.

Thanks,
Josh
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l4ent
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

JMPGuitars wrote:
Wed 05/20/20 5:38 pm
l4ent wrote:
Wed 05/20/20 3:19 pm
Isn’t my b+ pin 7, 375v?
No, that's your plate voltage, which is correct.

According to the schematic posted above, the B+ is supposed to be 385V, then drops to 370V after the first filter caps. B+ is the rectified voltage going to the filter caps.
l4ent wrote:
Wed 05/20/20 3:19 pm
I will consider adding screen resistors but as I understand it will affect the tone. I unserstand that pin 9 should be lower than 7 so this is a way to do it but looking at the schematic those voltages are actually about equal. I’m trying to understand why if everything is specd exactly to the layout why these mods are necessary or If something is off. As the transformer is specd the same and the parts used match the layout and schematics found on the net.
375 and 370 are not the same. The rule for pentodes is that the screen voltage should be lower than the plate voltage. If you want the correct tone for the amp, you must lower the screen voltage. The screen resistors also add a layer of protection.

Often these small changes in voltages are due to the tubes themselves. Other times it's a silly thing like forgetting to include screen resistors in a schematic.
l4ent wrote:
Wed 05/20/20 3:19 pm
I could use the zener diodes on the center tap to drop b+ Which would be a fun little thing but according to the charts the high b+ isn’t a problem, should I do this?

it’s that the screen is higher which is causing to redplate. But the og does not have screen resistors and buying the 2061 or ceriatone or other clone will not have screen resistors. I understand how adding them will help but concerned about tone as this circuit just sounds so good and they manage to run without em. Do I need to add them?
Your B+ is still unknown to us, so I don't know if you need to drop it. Your plate voltages are good right now.

If you're trying to capture the "OG" tone, then you need to pay attention to your voltages, not what clone amps have or don't have.
l4ent wrote:
Wed 05/20/20 3:19 pm
I also understand I can increase the sag resistor to 220 and go up from there to drop the b+ To better levels and create more sag / get a rectifier tube which could be fun to add there cause I think there’s space but then og does not have this, do I need to increase sag resistor? This will affect tone surely from the specd 22/30ohm.

Also increasing the bias resistor to maybe 220 should get it closer to where I need to be but concerned about rising b+. I’m thinking this is the next step?
No, this is backwards. Raising the resistor value will raise the voltage. You need to reduce the resistor value to drop the voltage. Try 150R or 130R. Measure your B+ before and after.
l4ent wrote:
Wed 05/20/20 3:19 pm
I’m also thinking that based on these responses, just dropping the screen voltage by adding these resistors (while yes changing tone a bit) will fix the red plate? Is that the simple solution to start?

I’m not sure where to start here.

If someone could answer those or help me understand further what the real “next step” is that would be great.

I see these “solutions” but it strikes me odd it needs to be so different from all of these specs I’m seeing. Shouldn’t it be achievable while being close to the product sold by these companies? Also since there seem to be many options I want to know the best route to take while maintaining this awesome sound I’m hearing
Steps as I've stated above:
1. Take your voltages, including your correct B+.
2. Adjust your cathode resistor to get to a better bias point.
3. Add 1K 3W screen resistors.
3. Take all your voltages again and share them here. Compare them to the schematic voltages.

Changing the screen voltages to the correct voltage is the right thing to do. I don't know that you would be able to perceive a tonal change. In any case, the correct voltage is generally the way it's supposed to sound.

The only specs that matter are the schematic. Making those changes will get you closer to those specs. That's what you want, and should give you the ideal tone, if you're trying to match the original. What people sell is an entirely different discussion, and doesn't fix your amp. A lot of people sell a lot of silly things for silly reasons.

Thanks,
Josh
I just figured that if they make it work without screen resistors there should be a way but I also don’t know anything lol

So far I’ve upped the cathode resistor to reduce redplating. You’re saying I need to bring it back closer to 130 from the current 160?

Does this help give all the volts needed? This is a user made schematic I found of a 2061x that I followed and the components match up to this. I could also make one off the layout if that would help. My voltages are in green [
77C84915-4D6B-4C92-AC81-D9702108B482.jpeg
Not sure if it makes a diff but the layout calls for 47uf 455v whereas mines got four 47uf 400v capacitors. Let me know if I need to remeasure the Pins.
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

l4ent wrote:
Wed 05/20/20 8:20 pm
I just figured that if they make it work without screen resistors there should be a way but I also don’t know anything lol

So far I’ve upped the cathode resistor to reduce redplating. You’re saying I need to bring it back closer to 130 from the current 160?

Does this help give all the volts needed? This is a user made schematic I found of a 2061x that I followed and the components match up to this. I could also make one off the layout if that would help. My voltages are in green [77C84915-4D6B-4C92-AC81-D9702108B482.jpeg Not sure if it makes a diff but the layout calls for 47uf 455v whereas mines got four 47uf 400v capacitors. Let me know if I need to remeasure the Pins.
If your tubes were worse before you raised the resistor, then you probably do need to raise the resistance higher. Just make sure to calculate the dissipation. You want to get your tubes to dissipate a total of around 20 watts. You're currently at 30W, which is way too high. I don't know what your target cathode current is for that circuit, but where you're at is high.

I would swap out those 400V caps for 500V. You never want to be that close to the voltage limit.
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

Am i not taking the HT reading right?
Screen Shot 2020-05-22 at 11.10.26 AM.png
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

l4ent wrote:
Fri 05/22/20 10:34 am
Am i not taking the HT reading right?
HT is the taps on the PT for your AC voltage that go the rectifier. Where are you reading those voltages? 18watt transformers are usually rated 290-0-290, and with modern voltage typically see 300-0-300 (assuming a center tap is present).

The B+ is that voltage rectified to DC. Your OT CT reading is usually the same as the B+ reading.
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by l4ent »

If it’s ac then I’m getting 303v
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Re: Marshall 2061 - Ceriatone Layout Redplate Help

Post by JMPGuitars »

l4ent wrote:
Fri 05/22/20 10:53 am
If it’s ac then I’m getting 303v
That is correct. Those HT wires going to the rectifier tube are the only AC readings taken at the tubes (besides the heaters, but that's usually taken at the PT).
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