R*E*D*D*ish mic preamp

[onailime]

Hi everybody this is my very first post

This is such a great place ! I'm learning more everyday thanks to you guys !... Maybe someday I'll have enough DIY experience to share it with you...

Anyway, I'm planning to build some kind of replica of the R*E*D*D amp and I've noticed on the schematic I've got, the B+ is regulated with two OA2 regulator tubes (150V) in series. I'm wondering what is the real impact of this design on the sound? Would it be night and day between this and no regulation?

Of course, the best way to find out is for me to try both, but I am just wondering if it is worth bothering with the OA2's...

Thanks for any reply ! :grin:

 

[Guest]

Val; here are few comments:

1. Rocket means a factory logo.
2. 6N1P was designed as a miniature replacement for 6N8S that was a Soviet version of 6SL7
3. Zeners are good noise generators.
4. Current sinks have higher dynamic resistance than simple resistors from +5V source. They may help to decrease hum if in case of resistors you have some. No more improvements.
5. Low dynamic resistance of a Zener shunted out your feedback, so you may proudly call it "An Amp with no GNFB", and remove everything associated with it (gain pot, switch, resistors, ...): anyway it does not work.
6. Emitter resistors provide a negative feedback by DC current so tubes from different boxes work equally well and live longer. With Zeners in cathodes working point will be less stable.

 

[Marik]

[quote author="Wavebourn"]
6N1P was designed as a miniature replacement for 6N8S that was a Soviet version of 6SL7
[/quote]

Are you sure on that? :shock:

I am not familiar with 6N8S, but AFAIK, the 6N1P is a frame grid tube with VERY different plate resistance, transconductance, Mu, plate current, etc. than 6SL7. The closest analog would be (apart from different ratings) ECC88/6DJ8.

 

[Guest]

[quote author="Marik"][quote author="Wavebourn"]
6N1P was designed as a miniature replacement for 6N8S that was a Soviet version of 6SL7
[/quote]

Are you sure on that? :shock:

[/quote]

Absolutely. 6N1P and 6N2P were developed to replace 6N8S and 6N9S that were Soviet versions of 6SN7 and 6SL7.

6N1P:

6N8S:

 

[Guest]

6N8S (6SN7GT):

6N9S (6SL7GT):

 

[bcarso]

6N1P: gm 7500 uS, mu 33. 6SN7: gm 2600uS, mu 20.

Your mileage may vary, but they seem to be worlds apart.

 

[Guest]

[quote author="bcarso"]6N1P: gm 7500 uS, mu 33. 6SN7: gm 2600uS, mu 20.

Your mileage may vary, but they seem to be worlds apart.[/quote]

You forgot about miles and kilometers. :green:


If to measure on the same currents/voltages I believe they will be close enuff though geometry is very different. Designers got an order to make small replacements; they made.

 

[Marik]

Obviously, originally there was a confusion between 6SL7 and 6SN7.

The scale of the posted graphs was kinda off. To get a better look at them go here:

http://www.amplimo.nl/download/6n1p.pdf

http://www.triodeel.com/6sn7_p4.gif

 

[Guest]

[quote author="Marik"]Obviously, originally there was a confusion between 6SL7 and 6SN7.
[/quote]

Sorry for misinformation: my typo. I meant 6SN7 (6SL7 was replaced by 6N2P)

 

[Marik]

That's OK.
Have you looked at the graphs I posted? From them it appears those tubes are way too different.

 

[Guest]

[quote author="Marik"]That's OK.
Have you looked at the graphs I posted? From them it appears those tubes are way too different.[/quote]

Anyway, 6N1P was not made as a military replica of E88CC, it is a tube made for wide range applications on low frequencies. Tapecorders, gramophones, audio amplifiers, TV sets, etc... "Sign of Quality" stamped on a photo of a tube means a civil usage; military tubes have a romb on them stamped.