6550 power tubes in an Ampeg V-4B?

[agedhorse]

In fact, I was thinking the same thing, it could be the PT or that infamous 6k11 or something else, i only hope is the bias only.

The output transformer's matching ratio may in fact be the limiting factor, along with the power transformer and bias (which will be quite different than for 6L6 tubes).

 

[Sunnampeg]

The output transformer's matching ratio may in fact be the limiting factor, along with the power transformer and bias (which will be quite different than for 6L6 tubes).

Hi thanks, yes I'm aware of it, I can definitely feel the extra heat in the amp and also a little more noise coming from the poor PT, and of course also my tech said that 6550s eat way more current than 6L6, I will try to receck the bias and make it colder if possible, if not I will go for the Tungsol 7581A, that should have very similar value to the original 7027A which are the stock tubes for a 70 s V4b, but i m wondering a lot of you guys says that you get more headroom with 6550s from your 70s V4b, how comes i have less with mine. Anyway, I will try with the bias thing again. And update here.

 

[agedhorse]

I never said you would get more headroom from 6550’s in that application.

Beware of what you hear from guys being accurate, there are a lot of crazy and inaccurate myths and falsehoods in the tube amp world.

 

[Sunnampeg]

I never said you would get more headroom from 6550’s in that application.

Beware of what you hear from guys being accurate, there are a lot of crazy and inaccurate myths and falsehoods in the tube amp world.

true, and I never pointed you when I was talking about the headroom, it was generic. Anyway, I completely agree with you, there are a lot of myths,
i m going to see the tech again tomorrow and he says to put the bias 50% and put ti at 21 w per valve but in that way am i going to have less output like less than 100 w like 84 85 watts if is like that than is going to be pointless having more headroom if you have put turn up the volume! i was just thinking.

 

[metron]

I had a few 70s V-4Bs at one time. One was modded for 6550 one had original 7027s in it. I definitely preferred the original layout.

The 6550s had different overdrive. Less grind than the 7027s. I also got the impression of more low end with 6550 but it wasnt significant. I did not get more headroom. It actually seemed less loud than the stock tubes because the 6550s had less midrange distortion. The 6550s were definitely hotter to the point of charring the vinyl on the back panel.

I realize Im late to the party and the amp has been modded. Just wanted to share my preference for the stock V-4B.

 

[Sunnampeg]

I had a few 70s V-4Bs at one time. One was modded for 6550 one had original 7027s in it. I definitely preferred the original layout.

The 6550s had different overdrive. Less grind than the 7027s. I also got the impression of more low end with 6550 but it wasnt significant. I did not get more headroom. It actually seemed less loud than the stock tubes because the 6550s had less midrange distortion. The 6550s were definitely hotter to the point of charring the vinyl on the back panel.

I realize Im late to the party and the amp has been modded. Just wanted to share my preference for the stock V-4B.

Thanks for the Info, ok I see ..but sounds weird to me that now my V4B with 6550s has less headroom with the 6L6, tad it started light crunch lean at 4 o volume, I mean 11 o'clock now it starts a 3 of volume, so at 10 o'clock.. I've used with Rick 4001 C64, so a passive bass with not much of an output. Yes, I've noticed a little bigger sound. But we will see tomorrow after rebias.

 

[agedhorse]

true, and I never pointed you when I was talking about the headroom, it was generic. Anyway, I completely agree with you, there are a lot of myths,
i m going to see the tech again tomorrow and he says to put the bias 50% and put ti at 21 w per valve but in that way am i going to have less output like less than 100 w like 84 85 watts if is like that than is going to be pointless having more headroom if you have put turn up the volume! i was just thinking.

You may get more power with less bias, it depends where on the load line it falls.

Thanks for the Info, ok I see ..but sounds weird to me that now my V4B with 6550s has less headroom with the 6L6, tad it started light crunch lean at 4 o volume, I mean 11 o'clock now it starts a 3 of volume, so at 10 o'clock.. I've used with Rick 4001 C64, so a passive bass with not much of an output. Yes, I've noticed a little bigger sound. But we will see tomorrow after rebias.

It may seem weird to you, but that's because you don't understand what's really going on and aren't understanding my comments either. It's not at all weird.

 

[Sunnampeg]

You may get more power with less bias, it depends where on the load line it falls.


It may seem weird to you, but that's because you don't understand what's really going on and aren't understanding my comments either. It's not at all wierd

Well, I do not have electrical competencies, of course, but if you explain in a very simple way, I may understand what you are talking about. It is very interesting

 

[agedhorse]

Because of the circuit design and output transformer choice, you may not get more power out of the amp when running 6550 tubes.

 

[Sunnampeg]

Because of the circuit design and output transformer choice, you may not get more power out of the amp when running 6550 tubes.

Yes I've got the same headroom as the 6L6 but a bigger soundstage.overall little more aggressive sound, the tech had to put it down to 50%, but now I do have a lot of HUM..and turning the hum balance only makes it worse.

 

[agedhorse]

You have run into the limitations of the circuit itself. This is not uncommon.

 

[beans-on-toast]

Yes I've got the same headroom as the 6L6 but a bigger soundstage.overall little more aggressive sound, the tech had to put it down to 50%, but now I do have a lot of HUM..and turning the hum balance only makes it worse.

You mentioned changing the power transformer. If it is closer to the power tubes, they may be picking up hum from the transformer. I don’t know if shielding or rotating the power transformer 90 degrees would help in this case.

If the tubes are not well matched, despite what the seller claims, badly balanced push and pull sides can result in hum. A simple test is to swap the positions of the power tubes and see if the noise changes. If you have an infrared temperature gun you can see if any of the tubes are running hotter than the others.

When running 6550’s in a vintage V4B, some add 1K 2W screen resistors pin-4 at each power tube R41, R42, R47, R48 to extend tube life. This comes with a little power loss.


I’d also check the 6.3V heater to ensure that the proper heater voltage is present with the 6550’s current draw.

A nice clean schematic:

https://www.talkbass.com/attachments/v4b-1974-schematic-pdf.2880196/

Service manual.

https://www.talkbass.com/attachments/v4-v22-service-manual-pdf.2880201/

Just to be clear, 6550’s should not be used in the current V4B reissue. It is optimized for 6L6GC tubes.

 

[Sunnampeg]

You mentioned changing the power transformer. If it is closer to the power tubes, they may be picking up hum from the transformer. I don’t know if shielding or rotating the power transformer 90 degrees would help in this case.

If the tubes are not well matched, despite what the seller claims, badly balanced push and pull sides can result in hum. A simple test is to swap the positions of the power tubes and see if the noise changes. If you have an infrared temperature gun you can see if any of the tubes are running hotter than the others.

When running 6550’s in a vintage V4B, some add 1K 2W screen resistors pin-4 at each power tube R41, R42, R47, R48 to extend tube life. This comes with a little power loss.


I’d also check the 6.3V heater to ensure that the proper heater voltage is present with the 6550’s current draw.

A nice clean schematic:

https://www.talkbass.com/attachments/v4b-1974-schematic-pdf.2880196/

Service manual.

https://www.talkbass.com/attachments/v4-v22-service-manual-pdf.2880201/

Just to be clear, 6550’s should not be used in the current V4B reissue. It is optimized for 6L6GC tubes.

hi as i ve said i ve a vintage v4b 1975 , yes but it did not made any terrible hum until yesterday , it has happened as soon as the bias was lowered.

 

[agedhorse]

hi as i ve said i ve a vintage v4b 1975 , yes but it did not made any terrible hum until yesterday , it has happened as soon as the bias was lowered.

Current sharing can change with bias, another side effect of lack of circuit optimization.

 

[Sunnampeg]

Current sharing can change with bias, another side effect of lack of circuit optimization.

You are suggesting optimizing the circuit for 6550s. I've read somewhere that someone added an extra PT to compensate for the insufficient efficiencies of the V4B PT. Or you were suggesting adding the screen resistor pin and all the rest, like Beens on Toast was mentioning?

 

[agedhorse]

You are suggesting optimizing the circuit for 6550s, I've read somewhere someone added an extra PT to compensate the insufficient efficiencies of the V4B PT

There are many, many things to consider, well beyond the PT.

 

[Sunnampeg]

Also, the funny thing about the V4b is that they leave the option for the 6550, but the PT is not enough for the 6550s and is too much for 6L6, it seems you can only stick to amp design and use 7027A.. there's no other way around.

 

[agedhorse]

How do you know that the PT is the limiting factor, or the only limiting factor?

You can’t, unless you do the calculations and understand how the circuit really works.

Your assumptions are typical of the incorrect conclusions made by hobbiests, DIY experts, and internet influencers who make unsubstantiated claims as fact.

 

[Sunnampeg]

well (the Hobbyst) my tech says that 6550s will stress the PT and 6L6 will get stressed by the PT

 

[beans-on-toast]

… my tech says that 6550s will stress the PT and 6L6 will get stressed by the PT

See page 3, performance package. The package consisted of the four 6550 power tubes and a set of bear claws that fit the tubes. A re-bias was required. They claimed 135W output power.

For V4B amps with a vintage power supply, they may or may not stand up to the current draw of the 6550 heaters. It depends on the health of the transformer. A replacement PT should be fine if it meets or exceeds the original specs.

The 7027A tubes will safely draw the current that they need. The amp was designed to accept 6550 tubes. The amp runs 540V on the power tube plates. This is above the 450V maximum rating of a 6L6GC. So it will stress a 6L6GC.

https://www.talkbass.com/attachments/ampeg-brochure-v4-pdf.741460/