Which Rectifier for Tweed Deluxe?

Yet another thread about our beloved Tweed Deluxe....

Just wondering what you guys have in your deluxes, and tell me if you prefer the tone you get from them.

Personally, I use a NOS 5V4 Sylvannia rectifier. I tried a NOS JAN Sylvannia CHS5Y3GT, but I don't think I prefer the tone what so ever.

The tweed deluxe already has enough sag, and 5Y3's sag too much IMO.

Maybe its just my 5Y3, but I think I prefer the tone and the slight increase in headroom that a 5V4 offers.

Yet another thread about our beloved Tweed Deluxe....

Just wondering what you guys have in your deluxes, and tell me if you prefer the tone you get from them.

Personally, I use a NOS 5V4 Sylvannia rectifier. I tried a NOS JAN Sylvannia CHS5Y3GT, but I don't think I prefer the tone what so ever.

The tweed deluxe already has enough sag, and 5Y3's sag too much IMO.

Maybe its just my 5Y3, but I think I prefer the tone and the slight increase in headroom that a 5V4 offers.

So if you put in a 5V4 do you have to change anything or is it just a tube swap?

So if you put in a 5V4 do you have to change anything or is it just a tube swap?

You need to re-bias the amp because it increases the B+ significantly.

Many players prefer to use GZ34s, as they increase the voltage a bit more over 5V4s and generally sound better.

Actually, my deluxe was made so that I can substitute a 5V4 for a 5Y3 without any adjustments at all. I can also swap any tube in the V1 as well.

What do you mean by any tube in VI? I don't think it is a problem in any amp to swap tubes in V1 as long as they are the same pin out ect and are of the same family of tubes that can safely be swapped like the 12a-7 family. . I also know that different rectifiers change B+ I asked as I never looked up a 5v4 to see what the specs are. Is it between a 5y3 and a 5u4?

Forgive me. Yes any 12A-family in the V1. I actually prefer a 5751 in the V1.

I think the 5V4 is somewhere in the middle of the rectifier family. Solid state offering very little sag, while 5Y3 offering the most.

Actually, my deluxe was made so that I can substitute a 5V4 for a 5Y3 without any adjustments at all.

And how was that feat accomplished?

Probably with some math ...

Probably with some math ...

Takes more than math to do that I'm afraid.

I think somebody was sold a little snake oil.

You don't think it's possible to choose a value of cathode resistor that would allow for acceptable operating points at the voltages those different rectifier tubes would provide?

Yet another thread about our beloved Tweed Deluxe....

Just wondering what you guys have in your deluxes, and tell me if you prefer the tone you get from them.

Personally, I use a NOS 5V4 Sylvannia rectifier. I tried a NOS JAN Sylvannia CHS5Y3GT, but I don't think I prefer the tone what so ever.

The tweed deluxe already has enough sag, and 5Y3's sag too much IMO.

Maybe its just my 5Y3, but I think I prefer the tone and the slight increase in headroom that a 5V4 offers.

THe JJ 5Y3 doesn't sag that much. Good compromise between sag and not.

sorry, double post

You don't think it's possible to choose a value of cathode resistor that would allow for acceptable operating points at the voltages those different rectifier tubes would provide?

Well, the 5Y3 has a voltage drop of around 60V @ 125mA

and the 5V4 has a voltage drop of around 25V @ 175mA

Math, as well as experience leads me to say "no".

Man, if I was going to jack the voltage in a cathode biased amp like a tweed Deluxe by going to a less lossy rectumfrier, I'd sure as hell be running the JJ 6V6s in there.

My tweed deluxe was made by craig collins of collins amplification. I too was concerned about the swap, but he builds em this way. I've switched back and forth with no problems what so ever. It only adds 6 more volts, which raises the headroom just a tad. If you want to get into all the technical mumbo jumbo, I'd say email craig personally at collinsamplifiaction.com

Sorry.....he doesn't sell any snake oil, just great amps.

The Deluxe is cathode biased so the bias will adjust itself if the B+ goes up or down as long as the bias is correctly set with the correct cathode resistor in the first place.

Increasing the voltage in any amp needs to be carefully considered. For example, if you have some NOS 6v6's in there and you change the 5Y3 to a rectifier with a significantly lower voltage drop you could fry the tubes. I speak from experience having burnt up a pair of favourite creamy Brimar 6V6's after a rectifier change.

6 volts shouldn't have much effect though.

Are the any audible signs of an NOS tube experiencing overvoltage but not yet dead?

I put an old 6V6GTY in my little Champion 600 amp and it sounds good but does tend to make a few creaky sizzling the first minute or two it's on. And even when it is running there is the odd hiss that isn't like normal single-coil noise and wasn't there with the stock Chinese power tube.

Of course allegedly the reissue C600 is only putting 360V on that 6V6 which doesn't seem high at all.

I apologize for the "snake oil" comment. That was uncalled for.

I also believe I may be wrong about saying it's not possible to set up the amp so it could be withing the acceptable plate dissipation range with both a 5Y3 and a 5V4. I was thinking more about the voltage increase with GZ34s, so I'm not on the correct page. The "6 volts" difference between using a 5Y3 and a 5V4 seems low, but I'll have to look into it.

The amount of range that these changes make is dependent, among other things, on how high the B+ is to start with. So we can to some extent be arguing apples, orange and pears.

I have a 5E3 out on loan. When that comes back in, and I get a few minutes, I'll do a quick comparison of data among the 5y3, 5V4, and GZ34, with no other changes being made to the amp. I'll post the numbers, and everyone can see and decide for themselves.

But Gee, if changing power tubes to ones with a different current draw necessitates checking and possibly correcting the bias of a cathode biased amp, is it unreasonable that changing the rectifier, which changes the plate voltage and current draw would necessitate the same?

From the Aiken Amps site (http://www.aikenamps.com/)

What about cathode-biased amplifiers?

Do cathode-biased amplifiers need to be biased? The short answer is yes. The cathode biasing method is self-regulating, to an extent, because increases in cathode current create a larger voltage drop across the cathode resistor, which in turn, creates a larger negative grid-to-cathode voltage, which counteracts the increase in current. The tube will reach a stable point of equilibrium and stay there. However, just as different tubes from different manufacturers will draw varying amounts of current in a fixed-bias amplifier, the same is true of a cathode-biased amplifier. For this reason, the bias should always be checked, even with cathode-biased amplifiers.

Checking the bias current in a cathode biased amplifier is easy, just measure the voltage across the cathode resistor and divide by the resistance value to obtain the cathode current. Note that if the output tubes share a common cathode resistor, you must divide the current reading by the number of tubes sharing the resistor. Note also that a common cathode resistor does not allow you to determine the individual currents of each tube, so if one tube is drawing more current than the other, you would not be able to determine which is causing the mismatch, and, in fact, you would not be able to tell there was a mismatch at all. You can add individual 1 ohm resistors from the cathode of each tube to the common bias resistor, but you must then measure across the 1 ohm resistors, not from the cathodes to ground, to determine the voltage drop, and thus the cathode current. You can also use individual cathode bias resistors on each tube. The value of the resistor will be double that of the common resistor if two tubes are used, or four times that of the common resistor if four tubes are used. Each resistor would also have to be bypassed with its own electrolytic bypass cap.

The difficulty with cathode-biased amplifiers is that the cathode resistor must be physically changed for another one of different value in order to change the bias current. Although it can be done, very few guitar amplifiers have adjustable cathode bias.

Cathode-biased class AB amps are usually exempt from the "70% rule", because their cathode voltage rises when a signal is applied, effectively reducing the bias, and shifting the amp further into class AB operation. This means you can bias them hotter than a normal fixed-bias class AB amp and the tubes will still survive. Having said that, you have to experimentally determine how hot you can bias them by finding out how far the bias shifts during signal flow.

SG - that last paragraph you posted from Aikens site seems to be pointing towards un-bypassed cathode bias. IOW, there's no cap across the resistor to shunt the AC signal. Without the bypass cap, a signal will develop across the cathode resistor, and act as local NFB.

As far as rect tubes go, raising the voltage to the Input Filter without changing the Input Cap, will cause the AC ripple current to rise as a percent of the B+ change. Ripple Current on the rect plates is what 'can' be a problem as the forward current through the tube can be up to 5X the load current on the filter. Although the forward curren is of a shorter duration, the higher the ripple, the longer the duration.

Just examining some of the other aspects here......

The sovtek 5y3 is a 5y3 in name only

see this discussion -

http://www.el34world.com/Forum/yabb2/YaBB.pl?num=1201230032/22#22

it's more of a 5v4

I know of no other current production 5y3; you have to go with a NOS tube; design for a 5V4, or use a dropping resistor

steven

But Gee, if changing power tubes to ones with a different current draw necessitates checking and possibly correcting the bias of a cathode biased amp, is it unreasonable that changing the rectifier, which changes the plate voltage and current draw would necessitate the same?
It isn't the current draw that kills some tubes, it is the voltage. Good high voltage tubes wouldn't have a problem - such as JJ's. Some tubes like the Brimar's, don't like to go over a certain voltage, which in my case happened when I changed the rectifier. From memory the voltage went from about 345V to about 379V and that was enough to do the damage.

Also, a standard 5E3 has a 250R cathode resistor which biases the tubes a bit hot anyway. FWIW Bruce Collin's at Mission Amps uses a 270R as standard and a 300R when using a choke.

5Y3, otherwise I'd get a different amp.

SG - that last paragraph you posted from Aikens site seems to be pointing towards un-bypassed cathode bias. IOW, there's no cap across the resistor to shunt the AC signal. Without the bypass cap, a signal will develop across the cathode resistor, and act as local NFB.

As far as rect tubes go, raising the voltage to the Input Filter without changing the Input Cap, will cause the AC ripple current to rise as a percent of the B+ change. Ripple Current on the rect plates is what 'can' be a problem as the forward current through the tube can be up to 5X the load current on the filter. Although the forward curren is of a shorter duration, the higher the ripple, the longer the duration.

Just examining some of the other aspects here......

No problem E Man. But where exactly are you seeing that he talking about un bypassed cathode bias?

SG - I read over that a little too fast, he's talking about the remnant charge held on the cap due to the few 10's of ohms of Xc + ESR.

...the remnant charge held on the cap due to the few 10's of ohms of Xc + ESR.

Man, I hate it when that happens :oops:

You guys are way above my pay grade on this stuff.