45 SET amp Project

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#128
vkung said:
I talked to Lundahl Last night
it seems that LL3720 is a good match. Mr Lundahl will make a 5K version for this project.
https://www.lundahltransformers.com/wp-content/uploads/datasheets/3720.pdf
From Lundahl
We are developing a new output transformer, LL3720 (6k : 8 ohms) specifically for single end application.By applying some tricks when winding the coils, the capacitive coupling between primary and secondary sections are minimized, which results in a better high frequency response. The transformer is suitable for triodes with plate resistance between 1 and 2 k, and thus matching DC currents from 30 – 40 mA up to 70 – 80mA. A data sheet for the LL3720 will follow shortly
Click to expand...
Happy Victor is back. Victory over health. (I'm just out of the ward too where I went with a broken heart).
The case looks good . .

My question is: does anyone already have experience with the LL3720 in Single End? I want to use it for a 10Y (which is said to be in the 45/50 family and maybe has a plate resistance of below 1.000Ω) and . . . I also have an older 25W/30W version of the 10Y.
Per Lundahl informed me yesterday they have that available. Looks great. No snake oil. Just great engineering. E.g. Look at the way the windings are spaced.
 
#132
Yes, I agree. The specs are strange. Because maybe there are various versions (I have the long plate one; as well as the standard short plate version). yes, old designs went for 16KΩ load, to the expense of HF (I had that); but I did get 5Watt out of the tube with ease.
But I should test the tubes some way (I do have a tube tester but it is not calibrated so it is just for a Go/No Go and for matching). :scratch2: A project almost by itself. Also the delta-Iplate/delta-Vg should be measured by hand (=S). See where it gets me.
Only then select the transformer.
 
#134
Thanks Euro.
Yes the higher plate wattage was clear to me as I got a high almost 5W outcome. I had a 5K transformer on the 4 ohm winding, and used a 20 mA trickle. Highs were not abundant but had a softness to them.

How I got the VT25A tubes? At a local military dump shop. They had bought a pack of airplane recievers, where a pair of V25A (7.5V) and Vt52 (5V) were used - in series. That means - their filaments could be used with on a 12V (=13volts) lead battery.

Then the question - as I remember it was stated - is the 10 (10Y/VT25/VT25A) like the 45 or 50? Now the feedback here was: NO. The Ri is mucho higher . . . So can't be used in this designg with a mere 5K transformer.
 
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#138
Hello Victor, Just love the 45 amp-using CX-345 cunningham's- I have 5 tubes and like the sound over the ST version. The amp is broken in now and I have ordered Canare 4S11G cables vs Belden 8471.. They say the Canare new G model is a winner--100hrs break-in! I sources 5 Altec 755A drivers which is enough. Getting good bass using hardwood bass reflex design on stands. My friends from Oramge County Audio Society were here over 3 weeks ago and really impressed with the setup. We re-positioned the drivers more in the corners toed at an angle and using an audio analyzer are getting 40HZ bass bumps---The amp is superior to any I have heard. The 45 to me is much better than any 300B-and I have heard many.

The 45 is very 3D and reviling while the 300B is slower and darker.

At 10 AM on the gain pot it's loud enough!! It's been a joy to know you!



Regards, R
 
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