Info about Collins and other old cool vintage tube preamps?

[scott2000]

'm actually looking for a wsm 15k/600 to try out in one of the new channels

I can check later... What's your 20?

 

[dawsonaudio]

I can check later... What's your 20?

I'm near Long Beach, CA.

 

[MidnightArrakis]

Here's a link of a photo of four channels of the gates sa-70's I built. The channels are powered by a 250 volt and 5 volt linear supply from International Power. I've got another three going with my last three altec 4722 mic input transformers. I have a bunch of audio bits and pieces that I inherited from a family member who was in the audio biz so I'm just trying to use them all up.

I'm actually looking for a wsm 15k/600 to try out in one of the new channels. I've currently got a channel with utc a-25, a-24 and two with cinemag cm-27101. If anybody has an extra/surplus one they could sell me, I'd appreciate it. Looks like the lead time is a month or more and want to get these other three finished.

Thanks,
Nate

Did you also do the sheet-metal work as well??? If so.....GOOD JOB!!!

/

 

[dawsonaudio]

Yeah thanks. Just a step bit and some aluminum

 

[MidnightArrakis]

I'm near Long Beach, CA.

>> That's a big 10-4, Good Buddy!!!

/

 

[MidnightArrakis]

Yeah thanks. Just a step bit and some aluminum

>> COOL!!! If you ever happen to need something done from "scratch" for one of your projects, you can let me know because that's what I do, as is shown below (both the mechanical chassis and PCB-designs):




>> I'm just finishing up an -- electronic module design -- for another member of this forum located in the UK.

/

 

[dawsonaudio]

Thanks. I appreciate it

 

[Cqwet Dbdfte]

When it comes to placing a power tx inside the same enclosure, these are rules that worked for me:
1. Distance is your friend. The further away from the most low-signal and sensitive part (this is often an input tx) your power tx is, the better.
2. Properly designed toroid power tx is your friend. The power field doesn't radiate as much with this type of transformers (IF they don't overload!)
3. Turning a power tx around and/or on its side can make a huge difference in the induced 50Hz hum and harmonics.

I tried shielding and it didn't help much. Besides, for shielding low frequency it's suggested to use special alloys that are very expensive. So for me, proper tx design and placement worked much better than shielding.

To reiterate some points:
Housing a PSU remotely is not always possible but is preferable.
SMPS trades 50/60 Hz fields for HF filtering, maybe easier, but different.
Toroids trumps (some use magnetic shields for these) , then C-core, R-core, semi-toroidal, with Ei lams at the bottom. Fluxbands, and shielding help a little, not much, orthogonal orientation can reduce coupling some.
Many old transformers were potted in steel cans, reducing external fields and vibration).
A lighter transformer load usually means less mechanical noise. Mechanical coupling is also a factor to consider.
Magnetic shielding at low freq is tough (expensive). The box layout may have to centered around this, and redone if needed. Aluminum is not much of a magnetic shield, unless maybe copper and nickel plated. Steel can shield, but also direct magnetic flux to where you don't want it.
My 2 cents...

 

[ze marcelo]

Hello everyone, I'm self-taught and I intend to build my first SA 70, so I'm studying a lot about electronic circuits, especially tube circuits, which also includes reading topics on different forums.
The next step for me will be to purchase some components and I would like to hear some suggestions from those more experienced. I've seen a lot of discussions about carbon composite versus metal film resistor, the same about polypropylene or polycarbonate capacitors, honestly it's a little confusing for me to decide.
So I would really appreciate it if you could share your choices in terms of wires, resistors and capacitors for this circuit. (brand and material).

Thank you all very much.

 

[Cqwet Dbdfte]

Carbon comp resistors is really old school, 5 -10% tolerances, if you can find them. High noise, high tempco, nah, stay away.
Metal film or metal foil if you have the budget.
Watch voltage ratings for those.
Wire-wound resistors have low noise, low tempco, bonus inductance filters HF. Larger.
Great for plate loads.
Caps, those choises are good. Use as high voltage rating you have space for.

 

[ze marcelo]

Hey Nate,
That is correct. The smaller the cap value the more bass This is the set I typically use and yours is not far off:

• .001 uf
• .0022 uf
• .0056 uf
• .008 uf
• .01 uf

Hi @beezer4 and @dawsonaudio , I'm planning to build an SA70 with the same modifications that beezer4 shared in the diagram above. I would like to know if you used this formula to choose the cap value for the bass control?


Thank you very much.