@mootej
I know that this is an old post but the link is rejected by Chrome and Firefox as being unsafe and insecure. If you have this PDF file, could you upload it here? It does look like it would be an interesting read.
Wow this thread is still going.
I am collecting parts to build a pair of these.
Anyone want to expound on why WE used a 10k output transformer vs the typical 6k "ish" we normally see with 6l6 ?
I am collecting parts to build a pair of these.
Anyone want to expound on why WE used a 10k output transformer vs the typical 6k "ish" we normally see with 6l6 ?
I tried to look at the schematic from the WE link, posted above, and now it is changed:
Western Electric: Technical Library
A lot of interesting stuff there.
Western Electric: Technical Library
A lot of interesting stuff there.
But this is not a "normal" circuit. The feedback taps are from the plates (one big reason for the "WE sound") instead of the output transformer's secondary and the feedback amount is not that high and having higher step down ratio provides lower output impedance and increases damping factors. If you only have 6K-ish transformers, you can compromise by connecting your 16 ohm speakers to the 8 ohm taps or 8 ohm speakers to 4 ohm taps.
Peerless 16309 output transformer in the Heathkit W5M has 10K primary so it's a good candidate for the WE 124 circuit. The Heathkit W4 also has 10K primary so it's a perfect candidate for 124 conversion, including all octal sockets. I hate building from scratch and if I still had the W4s, I would've modded them already!
Thanks for the input.
I am trying to get a handle in this before buying OPT's
Heathkit iron is pretty reasonable.
I am trying to get a handle in this before buying OPT's
Heathkit iron is pretty reasonable.
The outputs from the Heathkit EL84 amps might be good candidates. They are 10k primaries I believe and were used in amps rated 12-14W depending on the exact version. The 51-29 version by Stancor is reputedly the bestk and could possibly work for the lower powered version of the 124. I hadn't thought about this until just now.
The amps using the 51-29 were rated 14W. The low power version of the 124 says 12W so I think ok. Sort of depends on the bias currents required but I think the old EL84 Heathkits has fairly high bias current settings of about the same as the low power 124. I'll double check in a while when I get home.
Just looked at the Heathkit and WE schematics. In the 124 they output tubes are biased at 19V into either 250 ohms or 280 depending on the version. This is about 34-38mA per tube. The Heath UA-1 used the 51-29 output and the tubes were biased very hot at around 60mA. The laterf AA161 was rated as a 14W amp and the tubes were biased at 37mA per tube. Seems like the 51-29 should work in a 124. You'll have to decide if it's a good choice.
Some transformer specs and tests and each model includes the primary impedance so a diyer can repurpose them into suitable circuits, if they are sold in the used market. Obviously don't go around stripping a mint Marantz 8B irons!
I'm just spitballing here...
The more I look at the two schematics the more I think Heathkit W4 is an excellent candidate to modify into a pooman's WE 124 circuit.
Similarities/differences between WE 124 vs Heathkit W4 below:
Both have the same amount of tubes (5).
Both use octal tubes (6J7s need to add grid caps).
Both use rectifier tubes (5U4 vs 5V4).
Both use chokes (4H, 130mA vs 7H, 160mA).
Both plate voltages are similar (374VDC vs 370VDC).
The more I look at the two schematics the more I think Heathkit W4 is an excellent candidate to modify into a pooman's WE 124 circuit.
Similarities/differences between WE 124 vs Heathkit W4 below:
Both have the same amount of tubes (5).
Both use octal tubes (6J7s need to add grid caps).
Both use rectifier tubes (5U4 vs 5V4).
Both use chokes (4H, 130mA vs 7H, 160mA).
Both plate voltages are similar (374VDC vs 370VDC).
The W4 might very well be a good candidate if you have a couple of unrestored units.