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Thread: 407 plate voltage 5e3

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    407 plate voltage 5e3

    Hey lovely people of the world

    I have a 5e3 kit from triode and with the 20 watt PT im running 407 on the plates. I know this is a good deal higher than stock but is this acceptable? I calculated the bias of my tubes in this fashion- 22v across 250ohm cathode bias resistor/250 ohms * 1000= 88mA/2= 44mA/tube. Then 407*.044A=16.94watts. If this needs work any suggestions would be great. Thanks ahead of time

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    Bent Member Chuck H's Avatar
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    Why are your plate volts always high??? Where are you located?

    Is this the same amp you've been discussing in other threads?

    If you're using 6V6 tubes 17 watts diss at idle is too high.

    Is this PT from Triode intended exclusively for using 6L6 tubes in a 5e3 style amp? I'm not familiar with the Triode kits.

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    It may be I will have a check. ". For Power Transformer, you can choose between the 40-18021, 40-18017, or 40-18016. The 40-18021 is a standard Tweed Deluxe style PT, with a 710V CT HV winding. The 40-18016(120V) & 40-18017(120/240V) have a lower HV winding at 660V CT, increased current capability on all windings, which allows you to use different rectifier tube types, add additional tube stages, or upgrade your amplifier to use 6L6's!" I got the 40-18021 so im guessing this is why it is so high. is there a way to bias it down to under 14watts or should I just look to using 6l6s

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    oh and im just in Maryland lol my wall voltage is 117 on avg lol

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    or maybe a variable voltage regulator?

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    Don't forget the joker g1's Avatar
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    That sounds kind of average for that triode PT. From what I understand, the B+ will be higher with Sovtek 5Y3, so if that's what you have, a different brand rectifier might drop the B+ a bit.
    Are the 6V6"s JJ ? They should handle the high B+ better than others.
    Remember to subtract the cathode voltage from the plate voltage when calculating the idle current. So you would have .044 x (407-22) = 16.94W. (I see you had that solution, just correcting the typo).
    You should try to get it down to max. 14W by increasing the cathode resistor value.

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    Bent Member Chuck H's Avatar
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    Regulation is much further than you need to go. Though power scaling is popular so that might be an option. To keep it simple you could:

    1) Use the amp the way it is. 407V is high for a 5e3 but not too high for a pair of 6v6's. Actually your plate voltage will go up when you reduce current but tons of amps run 6v6's like this. So if you like the sound of the amp there's nothing to change other than the bias resistor. Try a 470 ohm for starters. You may need to go even higher. Look for 25mA to 30mA per tube.

    2) Use a big zener diode/s on the CT of the HV winding to lower the voltage. A pair of 20V 5 watt units in series would reduce your plate volts to about 370. The diodes should be mounted to sink heat and away from the filter caps.

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    1.) Replace any Sovtek 5Y3 with a NOS 5Y3 (I'm told the new-ish JJ would work as well, but NOS is almost the same price). The Sovtek doesn't have enough voltage drop, getting rid of it will lower your plate voltage 15-25 volts.

    2.) Increase the power tube cathode resistor to bias the tube colder. Do it after you replace the rectifier tube so you have your new plate voltage to calculate the resistor needed to get around 90-100% dissipation.

    The PT you picked has the uncompensated HT voltage. When Fender made the amp in the '50's, it was 110V from the wall to create around ~650V HT voltage; at 120V from the wall, that bumps up to 710V on the secondary...which is exactly how Classictone come up with that number, the used the exact same ratio of winds. The 660V transformer is compensating for the modern wall voltage to give 50's-era secondary voltages. There are different camps on which is better, "authentic '50's voltage" versus "50's amp plugged into modern wall," but the wild card is that crappy Sovtek 5Y3.

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    awesome suggestions guys I have a NOs 5y3 on the way and some 470ohm resistors lying around so I think im in a good spot . I have been thinking recently about voltage regulation coupled with regulated bias. If I did this do you think it would be a nice option for this amp to be able to handle a wider range of tubes? For instance when running 6v6 regulate down and bias accordingly and then when running 6l6 maybe regulate up a little and bias accordingly? I also like the idea of being able to get that sweet spot at lower volumes as I play to backing tracks in my room more than jamming with the fellas.

    Nice info on the PT too wyatt good to know this kind of stuff .

    In one sense im not to worried about keeping this amp in the 5e3 zone as 100% replica but I do want it to sound nice to my ears and others. At the time the 5e3 seemed like a cost effective way to get a really nice tube amp and get myself into the tube world at a decent price.

    I have not yet built a cab for my speaker and chassis yet so when I turn it up I don't get the true sound of the amp but possibly don't get as much distortion as a real 5e3? I wonder why this is/ maybe related to the way im sucking the life from my 6v6gts lol.

    After calculating the bias and dissipation (which im glad I did for me, my amp, and my tubes sake :0) I plugged some 6p3s (Russian 6v6) equivalents in and after jamming for about 10 mins noticed them on the serious verge of redplating!!!! I wonder why lol lol lol lol lol lol lol lol they are no where near as tough as the jj's so they were getting super swamped lol.

    Thanks again guys let me know if you have any other tips I love chatting with fellow music/amp lovers

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    Also If you guys could chime in on this question I wanna buy a celestion 12" 8 ohm speaker for my cab. Do you think 1 or 2 would work better? I had my eyes set on the Rocket 50 from celestion its 50 dollars at American music supply. Or would 2 16 ohm speakers work?

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    Bent Member Chuck H's Avatar
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    A good Celestion for a 5e3 would be the G12H Heritage. This according to resident 5e3 spert Bruce Collins. I haven't heard the Rocket 50. I get excellent 20W combo amp results with a Vintage 30 in a 1x12 combo that's made of poplar. 19"x22"x10". Breaking that Vintage 30 in was a year long sentence though. A bit harsh and upper mid heavy right out of the box but I'd do it again just because it sounds great when you finally work it in.

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    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Quote Originally Posted by redfoxblues View Post
    ...If I did this do you think it would be a nice option for this amp to be able to handle a wider range of tubes? For instance when running 6v6 regulate down and bias accordingly and then when running 6l6 maybe regulate up a little and bias accordingly? I also like the idea of being able to get that sweet spot at lower volumes as I play to backing tracks in my room more than jamming with the fellas. ...
    If you get it biased correctly with 6V6GT's and a 5Y3GT, then it will usually bias up correctly with 6L6GC's and a 5AR4/GZ34 without ever needing to use voltage regulation....but "your mileage may vary."

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    Senior Member CharlieP's Avatar
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    Quote Originally Posted by wyatt View Post
    1.) Replace any Sovtek 5Y3 with a NOS 5Y3 (I'm told the new-ish JJ would work as well, but NOS is almost the same price). The Sovtek doesn't have enough voltage drop, getting rid of it will lower your plate voltage 15-25 volts.

    2.) Increase the power tube cathode resistor to bias the tube colder. Do it after you replace the rectifier tube so you have your new plate voltage to calculate the resistor needed to get around 90-100% dissipation.

    The PT you picked has the uncompensated HT voltage. When Fender made the amp in the '50's, it was 110V from the wall to create around ~650V HT voltage; at 120V from the wall, that bumps up to 710V on the secondary...which is exactly how Classictone come up with that number, the used the exact same ratio of winds. The 660V transformer is compensating for the modern wall voltage to give 50's-era secondary voltages. There are different camps on which is better, "authentic '50's voltage" versus "50's amp plugged into modern wall," but the wild card is that crappy Sovtek 5Y3.
    I don't understand the high voltages with that transformer. @770 that is 385-0-385 virtually the same as my mojo 384-0-384. I do not get those high plate voltages. I don't have the numbers handy now but they are all normal.

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    Quote Originally Posted by CharlieP View Post
    I don't understand the high voltages with that transformer. @770 that is 385-0-385 virtually the same as my mojo 384-0-384. I do not get those high plate voltages. I don't have the numbers handy now but they are all normal.
    That seems a bit weird...

    384V on that mojotone should equate AC voltage before rectification..
    A 5y3 drops around 60V compared to diode rectification..

    So 1.4 x 384VAC = 537VDC - 60V = 477V before you starts loading it down more.. So maybe a 30V-40V drop when loaded so that should give you a minimum of ~ 437-447V DC on the first filter cap.
    Or use the 1.1 factor often seen for 5y3 recitifers.,, 384VAC x 1.1 = 422VDC when loaded down with ~ 100mA current draw. When you get above 125mA the voltage starts to drop fast with a 5y3...

    The classictone 5e3 power transformer 40-18021 is listed at 355VAC/100mA: with a 100mA load and a 5y3 rectifier the B+ is given as 396V DC which fits with the 1.11 factor for a 5y3 rectifier..
    A lot prefer the classictone 40-18078 which has two secondary outputs. The low voltage one (330VAC) gives a more correct 365V B+ which fits better with a pair of vintage 6v6gt tubes with a 250r bias resistor and 4.7K screen dropper.. The 396V DC B+ often biases the 6v6 tubes too hot with the stock 250r bias resistor...


    A DeArmond R15 (vintage 5e3 clone with huge transformers) uses a 250r bias resistor but a B+ of max 330-340V DC.. (schematic value)..

    With cathode biased output tubes high voltages are not really worth it.. Old vintage 6v6gt tubes are listed at 350V max plate and 315V max screen.. In a fixed bias you can go up to 415V like in deluxe reverb for added headroom and a cold bias.. try to bias output tubes with a resistor (cathode bias) in a high voltage scenario is not good,, You will need a higher value resistor to bias them cold enough and then you might start to get weird bias shifts when driving the amp... My rule is between 100r to 150r for a pair of EL84 depending on plate voltage or 250r to 375r for a pair of 6v6gt tubes depending on voltage.. If you need a higher value resistor to bias them in range (~80-100% of max dissipation) you need to drop B+ or use fixed bias (grid bias)...

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    hi chuck. i ^m start make a 5e3 amp but i have a 375 0 375 power transformer ,i can use this without problem o i need a bigger resistor.sorry for my bad english

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    The PT is the key, most important component in an amp, and you may have an unsuitable PT for a 5E3, or perhaps any 6V6 amp. It may be better suited to higher rated tubes in a fixed bias amp.
    Yes there are get arounds but they seem akin to hammering a round peg into a square hole.

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    Bent Member Chuck H's Avatar
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    What he said ^^^^^^^^^^^^^^^^^^^^

    What is the mA spec on that HV winding? That would be a good indicator of whether that PT is intended for a higher wattage amp. Which seems likely.

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    Check the video in post #1 & the reply in post #4 here:

    http://music-electronics-forum.com/t40643/

    Should clear up any questions of "can it be done & will it sound good?"

    Justin

    Edit: Bill Kirchen playing your amp doesn't hurt, either!

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    Last edited by Justin Thomas; 10-26-2015 at 06:03 PM.
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    Bent Member Chuck H's Avatar
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    The plausibility ends at some extreme though. I sim'd 375-0-375 on PSUD2 and the 5Y3 rectifier types produced 430Vp, but the toughest one just couldn't hang. I had to go to a 5u4 which produced 460Vp!

    I suppose you could add resistance to the 5u4 circuit to bring it down (a 100R drops it to 440Vp). There's the "string of zeners" voltage reduction too. I'd probably go with the added resistance just to soften the amp a bit more at those high voltages. I've read some posts here where 440Vp has been done with modern 6V6's. Lots of old Fenders run at 420+Vp with modern wall voltages. But all these examples assume a moderate AB1 bias point. And a "proper" 5E3 bias point is generally pretty hot. I wouldn't run ANY 6V6's hot with 440Vp.

    That amp in the link DOES sound good though Perhaps Mick will tell us just how much higher the voltages are on that amp.?.

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