45 SET amp Project

N

nickng

Member
Joined 2022
Victor, hope you recovered and this is wonderful news. Take your time and make this amazing. Hope it has great measured specs and also excellent sound too.
 
K

KT

Member
Joined 2003
This is great news, Victor!

I am interested in this project, for sure.

Thank you for making all this possible!
 
triode_al

triode_al

Member
Joined 2004
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.
 
E

euro21

Member
Joined 2004
Paid Member
triode_al said:
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.
Click to expand...
Are you sure?
The datasheet shows 5000R plate resistance even at 425V ... at 250V it's 6k.
Below 10k plate load it's "mission impossible" (high distortion).
 
triode_al

triode_al

Member
Joined 2004
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.
 
triode_al

triode_al

Member
Joined 2004
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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OtisCampbell

OtisCampbell

Member
Joined 2014
Paid Member
Also very interested in this project. I inherited a bunch of 45 and 2A3 triodes from my dad’s vintage radio repair side gig that I’d like to hear make music.
 
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