Hi,
After build a TW express with Hi-end Parts
I'm looking to built one with low cost parts... Just to see how it will perform...
So, Let see how the next build will sound !
I have look at this weeber transfo closest to what i need, if someone have something better, please tell me!
This output Trans show 6800 and (3400)
Why the 3400?
Any advise please for the right transfo
Thanks !
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Last edited by DaveWell on Tue Nov 10, 2020 1:52 am, edited 1 time in total.
The 3400 number is for running EL34, and the 6800 is for KT66 (I think...). I have used the Low Headroom version of this, and it sounds musically similar to the Classic Tone JTM45 transformer. Of course I have a tin ear, so...
I think that the Weber WPT30 will work
300-0-300 and 250ma is closest i have found a 7A on the 6.3V
and i dont find any match for Weber output transfo...
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Sorry...it seems like there are a couple prospective builds going on here, and I'm getting a bit confused. Is someone doing a budget Express, and someone else doing one with 6v6?
As far as calculating the voltage numbers for the PT, it depends on the type of rectifier you're using.
For a full-on budget Express, I'd be tempted to use the W025130 PT on the 540 tap along with that JTM45 OT (WOT45HHR or LHR, depending on the headroom you want). Might strain that PT, but you know me: Safety third.
I am piggy backing for information.
I am still in the cheap Express building phase and just want the basic EL34/6V6S option that the original had.
Namely the 6.6k OT and a power supply that is in the acceptable range.
I did some research and found out that if a PT spec sheet has combined voltage on the secondary taps(560v and 600v) you need to half that(280v and 300 respectively) and then multiply between 1.25-1.5, depending on rectifier used(Solid State vs Tube rectifier) and circuit load. A happy medium 1.31 multiplier to the half wave secondary voltage seems to be an accepted formula to get in the ball park.
So:
560/2 = 280 x 1.31 = 366.8vdc B+
600/2 = 300 x 1.31 = 393vdc B+ = Perfect for an Express build with the option to go even lower voltages.
The 300-0-300 taps are the ones that you want to use for an Express build. They should get you the expected 410 volts DC. For the output transformer, use the first, second and third tap with a 4, 8 or 16 ohm speaker to get a 6800 ohm reflected load.
For the OT, the https://tedweber.com/wot45lhr/ and using the 1st (32)16, 2nd 16(8) 3rd 8(4) will give me a primary of 6.8K and a secondary 4-8-16 ohm tap
Might need to get some Stand Up Bells for the PT.
I don't see End Bell Converters from Weber that are made specifically for the W022756 or the WPT30. Might have to contact them and see what they have or just install it laydown style if you have the room.
I suppose you could get 4 "L" brackets and 4 longer bolts from the hardware store to make your own?
Last edited by sonofmickel on Thu Nov 12, 2020 4:28 am, edited 1 time in total.
On the output transformer you need to use the secondary wires black, white, green and yellow to get 6800 ohms reflected from 4, 8 or 16 ohm speakers.
On the power transformer you use the red secondary wires for 300-0-300 volts center tap ground (red/yellow)
DaveWell, those standup bell covers will NOT work with the transformers you are looking at, those are for the 22798 transformers only. Look at the bolt spacing on the 22798's and compare to the other two transformers, not even close...sorry.
You might be able to get them to work? Maybe?
For the OT, the https://tedweber.com/wot45lhr/ and using the 1st (32)16, 2nd 16(8) 3rd 8(4) will give me a primary of 6.8K and a secondary 4-8-16 ohm tap
138.40$ USD plus shipping
We cannot much more cheaper
I would think you would want the White (4 ohm), Green (8 ohm), and Yellow (16 ohm) taps, if you're running at 6k8 on the primary.
On that PT, I'm guessing you'll get somewhere around 420 off the rectifier. A little high, but close.
