Tweedle dee PT question

[Kindablue]

Anyone think there would be a problem using the mojotone lower voltage (330v) PT for a tweedle dee 5e3?

[ChopSauce]

I also feared the B+ would be too low but I'm using a 320V(150mA) CT PT and my B+ seems already over the edge, using a GZ34 as a rectifier.

[Kindablue]

This is only 75ma. Yours is 150ma? The one im talking about is the MOJO756EXLV ...has a CT and 330v/75ma on each red tap.

[ChopSauce]

75mA isn't very high. You may expect that your B+ will be lower than mine (largely over 400V) under load, but I don't know how much...

All I can say is I never read about someone having too low voltages on his tweedle dee, maybe dut to the GZ34?

If you already have the PT or are ready to sell it if it doesn't suit, that seems worth a try.

It should be a bolt on fit and if you connect it without cutting the wires there shouldn't much to loose, right?

[Kindablue]

Totally. My only question was should I try to find a 350v pt (mercury makes one) to have ready as a backup just in case.

[wpaulvogel]

Ever thought about a Hammond 290BBX

[Craig B]

Mojo's way of describing the specs is confusing to me. I "think" they mean it is a 330-0-330 at 150 ma. If I were building with 6V6GT power tubes, I would not want any higher voltage or amperage than that. I will be curious to see what others think.

[Kindablue]

I know...here's the spec sheet for it. Tell me what you think.
https://imgur.com/gallery/0zNrBFB

[sluckey]

I think mojo described it clearly. Think about the rectifier circuit. Current can only flow in half the secondary at any time so the two currents are not gonna be additive. 75mA sounds reasonable for each half of the winding, but that's cutting it very close. Heck, my 5E3 output tubes draw .072mA with 335V on the plates!

[Kindablue]

I ordered a 350v pt from mercury to be safe

[Kindablue]

Couple of other questions:
Regarding PI 10k pot
Does anyone here have any experience adjusting the 10k PI pot? How did you take resistance measurements...between the lugs of the pot and the resistor each lug is attached to(besides the wiper)? I assume you have to do this with the amp on...is this safe? I understand the voltages involved here ate only around 10v but still. Did you start with the pot centered in the middle etc?

Regarding inputs
Did anyone use both high and low inputs on normal channel? My chassis is set up for 4 inputs like a normal 5e3 and I still wouldn't mind being able to jumper inputs. Am I missing something by putting 2 68ks in and using both inputs in place of the one 33k resistor and just using one input on channel 1?

[ChopSauce]

I see no reason why wiring the four input "à la" 5E3 shouldn't be fine.

I ordered a 350v pt from mercury to be safe

Isn't your B+ a bit high - even for a Tweedle Dee ?

I truely wonder what it is, that and the rectifier you used...

[martin manning]

I think mojo described it clearly...

But that is an unconventional way to specify current capability for a HV secondary designed for a two-phase rectifier.

Couple of other questions:
Does anyone here have any experience adjusting the 10k PI pot? How did you take resistance measurements...between the lugs of the pot and the resistor each lug is attached to(besides the wiper)? I assume you have to do this with the amp on...is this safe? I understand the voltages involved here ate only around 10v but still. Did you start with the pot centered in the middle etc?

You should see around 45V at the top of the trim pot. Make a wooden screwdriver out of a chopstick or a bamboo skewer to adjust the trimmer safely. You can look at the PI balance with an oscilloscope, but if you don't have one just start with the trimmer at mid range and set it where it sounds best to you. If you didn't see the memo, the 1M grid resistor on the PI should be a 10M.

Did anyone use both high and low inputs on normal channel? My chassis is set up for 4 inputs like a normal 5e3 and I still wouldn't mind being able to jumper inputs. Am I missing something by putting 2 68ks in and using both inputs in place of the one 33k resistor and just using one input on channel 1?

Should be fine, and I think most people are using the 4-input 5E3 arrangement. The original was a modded 5B3, so one input triode uses two jacks in the typical high/low setup and the other is fed from the third jack with a 33k, making it look like a high input.

[Kindablue]

Ok cool. So the 1M is actually 10M. But shouldn't I be able to measure resistances between the pot and the 10m resistor and between the pot and the 56k resistor? Looks like it should be 3.5k between the 1pm and 6.8 k between the 56k and the pot? Am I confusing something? Is this a measurement I should strive for after starting with the pot in the middle?

If doing it by ear, what are you listening for exactly...bloom? Just where it sounds best in general...and at what volume/gain?

Sorry for all the questions.

[Kindablue]

I've also heard some folks were using a 5k 5watt resistor in place of the 4.7k dropping resistor?