lower wattage in 5E7A tweed pro?

[Bluefinger]

ok, here's the situation. I have a self built tweed pro which I like a lot but sometimes i could use a dirtier sound out of it. I have tried different approaches from attenuaters to fumbling with the -fb loops and so on. It's all kinda ok but not quite what I would like to hear. Then it happened ... I played it right after I switched on the amp. First there is no sound and then for a second or two before the rectifier tube delivered it's full voltage it had the tone I was looking for ... that soft old school bluesy grind. So I wonder, is there an easy way to achieve this effekt? How can I drop the voltage (would it be save anyway ... I guess so)? I could use the 240 volts lead on the power tranny instead of the 230 but hat's not nearly enough. The ideal solution would be a switchable situation or at least a tube swap ... what about using a weak rectifyer tube like a 5Y3 in that circuit? Would that help and is it safe (it runs a 5U4G now)?

thanks!

[Chuck H]

Well, a few things are happening in those moments between flipping the power on and the amp reaching optimum operating condition. The rectifier tube may be delivering a little less voltage, but it also isn't delivering it as well because the filament isn't fully heated. How this may change rectifier function I don't know. But it'll probably be as big a difference to the amps playability as the actual voltage. And then there's the filter caps, which are charging at this time with the rising voltage. They can't do their job properly before that happens so instead they would have been filtering poorly. That means ripple superimposed on the tone and creating sum/difference distortions. Then there's all the other tube filaments that wouldn't be at full temp either. This reduces a tubes efficiency and at worst creates additional distortions relative to a starved space charge of electrons around the cold cathode. There would probably be significant changes to the individual tube bias-es too relative to how the supply is arranged.

My point is, what you heard may not be re-creatable without tremendous trouble and possibly working outside of safe operating parameters.

By tremendous trouble I mean that beyond reducing plate voltage you may need to go so far as to reduce filaments to the lowest safe operating voltage. And I'm not even sure what that might be for a rectifier. Install very small filter caps. Which would be awful for everything but that one tone. Skew the bias as far as possible that doesn't put the amp in danger in any playing conditions. And maybe even fudge preamp tube bias as well. And most of these parameters aren't usually used for tone shaping so getting it all lined up would become a virtual impossibility.

You can at least try the reduced plate voltage. There are discussions here about "power scaling" that can be referenced. That would allow you to brown down just the HV rail. Bias voltage needs to be monitored and at least kept in a "safe range" some of the power scaling circuits are better about this than others. And you don't really want to brown your filaments by too much, so leaving them out is probably for the best.

[pdf64]

What amp have you built? 5E7 is a Bandmaster, 5E5A is a Pro.
It would be best if you could link to the schematic used; any divergences from the schematic, eg was a pi HT filter really used to feed the OT CT?
And link to the specs of the transformers used, as eg the OT impedance isn't noted on the schematic.

Yes, try a 5Y3, provided that the reservoir cap isn't much above 22uF, but be prepared for that change not being as effective as you may be hoping for.
Best to use a vintage made 5Y3 or JJ, as the Sovtek are reputed to be non con-formant to 5Y3 bogy characteristics, putting out excessive HT Vdc.

[EFK]

What are being sold as soviet 5Y3 actually compare almost identically to a 5V4 in a 5Y3 shaped bottle. Not good for 5Y3 amps!

[Bluefinger]

Well, a few things are happening in those moments between flipping the power on and the amp reaching optimum operating condition. The rectifier tube may be delivering a little less voltage, but it also isn't delivering it as well because the filament isn't fully heated. How this may change rectifier function I don't know. But it'll probably be as big a difference to the amps playability as the actual voltage. And then there's the filter caps, which are charging at this time with the rising voltage. They can't do their job properly before that happens so instead they would have been filtering poorly. That means ripple superimposed on the tone and creating sum/difference distortions. Then there's all the other tube filaments that wouldn't be at full temp either. This reduces a tubes efficiency and at worst creates additional distortions relative to a starved space charge of electrons around the cold cathode. There would probably be significant changes to the individual tube bias-es too relative to how the supply is arranged.

My point is, what you heard may not be re-creatable without tremendous trouble and possibly working outside of safe operating parameters.

By tremendous trouble I mean that beyond reducing plate voltage you may need to go so far as to reduce filaments to the lowest safe operating voltage. And I'm not even sure what that might be for a rectifier. Install very small filter caps. Which would be awful for everything but that one tone. Skew the bias as far as possible that doesn't put the amp in danger in any playing conditions. And maybe even fudge preamp tube bias as well. And most of these parameters aren't usually used for tone shaping so getting it all lined up would become a virtual impossibility.

You can at least try the reduced plate voltage. There are discussions here about "power scaling" that can be referenced. That would allow you to brown down just the HV rail. Bias voltage needs to be monitored and at least kept in a "safe range" some of the power scaling circuits are better about this than others. And you don't really want to brown your filaments by too much, so leaving them out is probably for the best.

ok, thanks ... hmmm. I think I'll try some of the simpler approaches first

[Bluefinger]

What amp have you built? 5E7 is a Bandmaster, 5E5A is a Pro.
It would be best if you could link to the schematic used; any divergences from the schematic, eg was a pi HT filter really used to feed the OT CT?
And link to the specs of the transformers used, as eg the OT impedance isn't noted on the schematic.

Yes, try a 5Y3, provided that the reservoir cap isn't much above 22uF, but be prepared for that change not being as effective as you may be hoping for.
Best to use a vintage made 5Y3 or JJ, as the Sovtek are reputed to be non con-formant to 5Y3 bogy characteristics, putting out excessive HT Vdc.

Sorry, I got that mixed up. But apart from the speaker configuration and -fb resistor values they (and the 5F4 Super) are the exact same amps. I have switchable - fb loops anyway so it doesn't makle a difference which one you are looking at

Heres a schematic that I referred to: http://www.turretboards.com/layouts_..._super_5f4.gif

[Bluefinger]

I should have a TAD 5y3 or two available. I'll try one of these

[Jammin'John]

5R4

On my Tweed Pro I run a 5R4 and a less efficient speaker.

JJ

[olddawg]

So you have access to a variac? You might try browning it down a bit to see if you do get the sound you want that way and then take some measurements. If the filament supplys get really low you can all was sub a separate transformer for test.