[L0rdGwyn]

So I literally begun the journey yesterday and I will not be using the Elma switch as posted before, @L0rdGwyn no change in the instructions in this post: https://www.head-fi.org/threads/aegis-diy-tube-headphone-amplifier.965530/post-17596500 ?

Main pcb board ready, got all parts except the chassi plates from a local laser cutting shop, hopefully get them next week, though then powder coating at a different shop…

Yes there is a change - pins 2+10 are the signal output where 5+7 will be ground. It's a matter of flipping which lead is signal and which is ground either on the primary or secondary of the output transformer.

 

[L0rdGwyn]

I was reading the post and he mentioned the elma switch and my first reaction was, "NOOOOOoooooooooooooooo I don't want to solder a new elma board!!!!"

I think I can handle flipping these unsoldered wires. It gives me an excuse to test the readings on the 6889 tubes anyway, which I've been putting off.

Oh if it were that complicated, I would say it isn't even worth doing! But given it's so simple and not what I had intended, I felt I should point it out. There are amplifiers on the market that have reversed polarity by the very nature of their circuits (any cathode follower OTL for example), but since we can correct the polarity here with the output transformer, might as well do it.

 

[goldwerger]

Oh if it were that complicated, I would say it isn't even worth doing! But given it's so simple and not what I had intended, I felt I should point it out. There are amplifiers on the market that have reversed polarity by the very nature of their circuits (any cathode follower OTL for example), but since we can correct the polarity here with the output transformer, might as well do it.

Who, which community member here will now be the first to implement a polarity switch?

 

[Toonartist]

Who, which community member here will now be the first to implement a polarity switch?

Done... before I consumed the beers I bought as payment for the job!

I haven't listened properly to it yet.. just a quick check. That'll come a little later this evening!

 

[mattiastomas]

Who, which community member here will now be the first to implement a polarity switch?

I switched it this morning. It’s not a huge difference but I do perceive that it does sound better.

 

[Toonartist]

I switched it this morning. It’s not a huge difference but I do perceive that it does sound better.

Interesting. Looking forward to listening to it this evening!

 

[henrix]

Yes there is a change - pins 2+10 are the signal output where 5+7 will be ground. It's a matter of flipping which lead is signal and which is ground either on the primary or secondary of the output transformer.

thanks so just to be clear, I can solder the 4.7k resistor between pin 5 and 2?

And the polarity as below and directly to the headphone jack?

 

[L0rdGwyn]

thanks so just to be clear, I can solder the 4.7k resistor between pin 5 and 2?

And the polarity as below and directly to the headphone jack?

Yup, you got it.

 

[L0rdGwyn]

I've really been enjoying the Brimar 5R4GY rectifier in Aegis. Been a while since I compared them, but I felt it added a little more low end heft relative to the Philips GZ34. I think it's worth trying. They are somewhat expensive though.

 

[DenverW]

I've really been enjoying the Brimar 5R4GY rectifier in Aegis. Been a while since I compared them, but I felt it added a little more low end heft relative to the Philips GZ34. I think it's worth trying. They are somewhat expensive though.

I picked up an rca 5r4gy which was a little less expensive. I’m not sure how I feel about it yet. I’m still using the mullard gz34 black base notch plate.

I also had a chance to fix the polarity wiring, as while I did I tested the readings for the 6889 power tubes. With the mullard gz34 rectifier I got 246 for power tube plate voltage (step 10) 237 for input tube plate voltage, and 11.4 for power tube cathode voltage. When I put in the 5r4 rca tube the cathode voltage dropped to 9.85.

 

[L0rdGwyn]

I picked up an rca 5r4gy which was a little less expensive. I’m not sure how I feel about it yet. I’m still using the mullard gz34 black base notch plate.

I also had a chance to fix the polarity wiring, as while I did I tested the readings for the 6889 power tubes. With the mullard gz34 rectifier I got 246 for power tube plate voltage (step 10) 237 for input tube plate voltage, and 11.4 for power tube cathode voltage. When I put in the 5r4 rca tube the cathode voltage dropped to 9.85.

That will work, 11.4V on the cathode corresponds to a bias current of 32mA and a plate dissipation of 7.8W, well within tolerance. Cathode voltage drop with the 5R4 is due to its higher Vdrop compared to the GZ34, so the plate voltage and bias current will go down, which is fine. As I recall, the Brimar is a step ahead of the RCA 5R4, but it's been a while since I compared them.

The Brimar has a very nice internal construction.

 

[goldwerger]

I've really been enjoying the Brimar 5R4GY rectifier in Aegis. Been a while since I compared them, but I felt it added a little more low end heft relative to the Philips GZ34. I think it's worth trying. They are somewhat expensive though.

Same as @DenverW I also have an RCA 5R4GY which I replaced with Phillips Miniwatt (my case) GZ34

was going to ask how you thought the Brimar 5R4GY compared as your answered popped up already.. I guess will have to try some time...

 

[DeviousEnigma]

Here's a source for carbon comp resistors: https://www.tubesandmore.com/products/resistors

Which resistors were previously the carbon comp ones which are not carbon film in the BOM?

 

[L0rdGwyn]

Which resistors were previously the carbon comp ones which are not carbon film in the BOM?

R22, R23, R24, R25. There are many sources for carbon composition resistors outside of Mouser... but again, it will not make a significant performance difference, so not worth pursuing a different source. I've substituted carbon films in the BOM which will work just fine.

 

[AnyDave]

R22, R23, R24, R25. There are many sources for carbon composition resistors outside of Mouser... but again, it will not make a significant performance difference, so not worth pursuing a different source. I've substituted carbon films in the BOM which will work just fine.

How do you feel about metal films? I typically prefer those to carbon film as they are lower noise.