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Western Electric 124 amplifier

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I also got a chance to check the AC balance with a multimeter and noticed level of one phase is lower than the other by about 10% which is not surprising in a floating paraphase circuit if the grid resistors like R7 and R8 are identical (100KΩ) so in a DIY amp, I would tweak one resistor's value to achieve AC balance, say, making R8 to be 110K or 120KΩ or install a trimmer resistor in there if you want to be precise.

We hooked it up listening to mono and subjectively the sound was glorious!

Again, anybody has any thoughts on the function of C10/.02μf?
 
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The one with no cap has a blown power transformer so was not able to listen in stereo, hence the mono audition of only one damp. I did disconnect the cap and check AC balance and did not affect the level but I was not able to AB the sound as I only had few hours to play around with them and they are returned to his suburban home now. Maybe next time.

The 124 is a worthy circuit to clone and satisfy the DIY bug and with some minor adjustment it can be tweaked to your heart's content. It's a great sounding 6L6 amp and the other amp in its class, in my opinion, is the rather rare Altec 126 and 127 amps.
 
Hi Roscoe,

It's good to hear your version turned out well. What changes if any did you make to the standard 124 circuit?

I used 77s for the drivers, mostly because I have a dozen or so NOS 77s. I left out C7/R12/C11 mostly because at the time I didn't know that R12 wasn't a pot. With the power transformer I used, B+ is between the 12W & 20W values.

Roscoe
 
Interestingly enough, US military tests claims Stancor and Peerless trannies much higher in quality than WE. As we all know, measurements are not everything and much of a quality of a trannie couldnt be measured respective some trannies that dont measure well sound very well. WE seems to be such a case, their trannies were all very limited in bandwith but are nowadays the highest priced and praised. Did someone a shootout with Peerless, WE, Stancor or Acrosound in a Williamson-style amp? Is it all "WE-hype" of asian audio fanatics or do they sound indeed so much better than their competitors from GB and USA?
I have this question in regard of some asian WE-copied trannies for single ended and PP, which pop up on ebay and claim to be exact copies.
 
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There is something about certain antique components, audio transformers in particular, that we may not understand well.

Anatoly Likhnitsky, a late maverick audio designer from Russia, had particular affection for pre-war Telefunken iron. He claimed that using just a single Tehefunken transformer imparts otherwise unachievable goodness to sound.

I have a 1934 Rauland 2A3 amplifier whose original output transformer does not have any interleave - just secondary on top of the primary. I decided that upgrade was in order, and replaced it with a transformer of modern design. With this "upgrade", the magic sound of the amplifier was gone. So, the original transformer went back in, which restored the harmony.

I am much enamoured with 1920s-30s interstage transformers made by Ferranti of England. These transformers and 01A type tubes are a match made in heavens.
 
What do you mean with AM-radio? A tuner and a WE pre-amp section to follow? I wasnt aware that WE did build audio tuners.
I do think they are famous for their components which were build with the best materials. Being it tubes or transformers. Everything else they used to buy from third party (meaning KS type of parts).
 
Consider the bandwidth of the material available when this stuff was built. A 755A was considered "full range" but by today's standards is certainly not!

When you pair these with the WE A171A output transformers, you'll get wonderful midrange but not a whole lot of bass and a distinct absence of treble.
 
I was able to glance at the innards of my friend's pair of 124E and noticed that those parts don't exist in that version. His amps do not appear to have been modified. So I take it they are not essential to the circuit. Parts R18 and R19 are also not there. In a DIY project, I guess they're not necessary, given one will use different output transformer. It is then a pretty straight forward design.

My only question to members here is that is C10/.05μf value high enough to negate the function of the feedback since it's connected to input 6J7's screen-grid and ground? What does it do, really? In one of my friend's amps, it does not even exist! :scratch:

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Directdriver, if you are still following this thread, I found the answer to your question about the purpose of C10 (0.02uf) which runs from one of the feedback legs to ground. I located a WE technical manual for the 124 online (I printed it out but I don’t have a link for the source). This manual says:

“Condensers C7, C11 and resistance R12 form a protective network to guard against high frequency surges with an attendant possible breakdown of the final stage tubes. As this network tends to reduce somewhat the amplifier gain at higher frequencies, C10 has been provided in the feedback circuit to compensate for this and thus bring the overall gain at the various frequencies to within the required limits.”

Since you mentioned one of your friend’s amps didn’t have the C7–C11–R12 network and one of the amps didn’t have C10, I am betting it was the same amp where all of these parts were deleted. For DIY purposes, I am pretty confident they can all be eliminated.

It’s been a long time since I said on this thread that I was going to build some amps with the 124 circuit, but that time has finally come. I have most of the parts I need and plan on starting it soon. What motivated me to finally get going is that I built a pair of PP 6L6 amps a few weeks ago with a somewhat similar circuit and they are sounding really good. These amps are similar to the 124 in that they use a floating paraphase inverter and run the 6L6GC tubes in tetrode, but that’s where the similarity ends. Mine have a 6SN7 gain stage cap coupled to 6SN7 drivers, and there is a small amount of global NFB. The WE 124 circuit should make an interesting contrast by eliminating one gain stage and using feedback from the 6L6 plates rather than the OPT secondary.

I still have to decide what OPT to use with the 124 circuit. I have several options at hand—-Acro TO-330 (3.8K), Sansui 1000A outputs (5k), Chicago outputs from Eico HF-20 (6.6K), and Hammond 1650 R (5K). All of these are lower impedance than the 10K used in the 124 but should still work well.
 
I found something else in the 124 manual that may be of interest. This concerns the value of the capacitors in the feedback loops C8 and C9 which are each 0.05uf. The manual says:

“C8 and C9 also provide low frequency equalization permitting a less expensive input transformer to be employed. The equalization amounts to about 1.5db at 35 cycles.”

For a DIY build, which won’t use an input transformer, leaving C8 and C9 at the .05uf value will cause a bump in LF response. That doesn’t particularly bother me but it’s worth noting.
 
I have owned many We 300B amps; I intended to rewire them; BUT luckily but found out they are so valuable; I built many many wonderful amps on the proceeds, best of all the amps running 811A/572b. The WE 300b low powered amps drove huge very sensitive speaker in big cinema’s running on a few watts The boxes for the bass horns where as big as a small room with huge HF horns. I use horn loaded 105DB speakers not as big as the WE horn speakers
 
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