Cross-referencing old transistors...??

[jetboatguy]

Old transistors:

input section has:
2N508A x 5
2N527 x 1

output section has:
2N4250 x 4
2N697 x 1
2N527 x 1

I was wondering if I could swap some old transistors and sonically improve my mic preamps with modern transistor replacements... is this a waste of time ?

I have 4 x Scully 280 channels that I've overhauled recently... so far I've wired in a newer power supply, 24VDC from McCurdy Radio Industries and I've also re-capped every single electrolytic in each Scully amp/unit... aprox' 110 caps !!

Here's the schematic to the Scully 280... notice the squares with broken/dotted lines in the scematic, each Scully amp has 3 removable audio PCB cards that plug into it's own edge connector... the (record amplifier card) holds the mic pre circuit with some transistors and eletrolytic caps... the line out driver section is in the (playback amplifier card)... and the (bias/erase oscillator card) is removed from the unit, it has no function to the mic preamp duties.

http://web.telia.com/~u31617583/Scully%20280%20audio%201.jpg

http://web.telia.com/~u31617583/Scully%20280%20audio%202.jpg

 

[jetboatguy]

Bump...


Hello, anybody out there ?

 

[jetboatguy]

I see what your sayin'... I would never want to de-rail a classic Rolls Royce.

although, if I get other Scully PCB cards ( they sometimes appear on ebay from time to time) the cards can easily be swapped from behind each amp unit, it would be interesting to see what sound/flavor I could get from other modded cards.

 

[jetboatguy]

thanx for the encouragement,
I think you misunderstood the cap swaps (my bad!)
I meant a total 110 electrolytic caps in all 4 Scully amps were replaced,
the McCurdy power supply seems to be holding up fine.

 

[CJ]

I just looked at these old RCA's for the first time. 2N220! Lordy. Where can I find those?
If you know that there are threads on old transistors, just say "search, lazybones!" otherwise I will play stupid and hope for repeat posts from the vintage Germanium freaks. And I know your out there!

 

[jetboatguy]

The Scully has some RCA transistors on the preamp board... but according to the schematic, they are not 2N220 you speak of... what's the big deal with old Germanium transistors ?

I have a 1964 McCurdy mixer with silicon transistors on all the PCB boards, and these preamps would eat the Scully's for lunch.... much more detail and really fat sounding.

 

[CJ]

Sorry, these are BC71 and 73 mic pre's. Some with Ge, some with Si.
Should have clarified.

 

[Flatpicker]

Hello jetboatguy, and welcome to The Lab!

 

[jetboatguy]

Thanx, I'm learning lots with this forum,
over the years I've done lots to maintain or modify my studio's recording gear, sonically for the better hopefully... and few pieces of old gear/handyman specials along the way.
I still consider myself a hack when it comes to the DIY from scratch projects... but today my ears really know what they like to hear in the studio... I'm willing to take my soldering iron further than it's ever been before to achieve this within my budget.

 

[jetboatguy]

[quote author="CJ"]Sorry, these are BC71 and 73 mic pre's. Some with Ge, some with Si.
Should have clarified.[/quote]


BC7's... Are those old RCA broadcast mixers...?

I've never really seen one up close.... I'm in the land of McCurdy's and Ward Beck's

 

[CJ]

Yes, I believe out of the old mixers.

Hitchiker was kind enough to send me the hard copy schematic and manuals for both the BA-71 and BA-73, if anybody is interested, I could scan them.

 

[jetboatguy]

SO... I've put these 4 Scully pres through it's paces recently, they sound pretty good... although I'm hearing some slight differences between channel to channel and thought it might be time to tackle the transistors, to get all 4 Scully's closer to match.

I did a cross reference at the NTE website for all these transistors... it appears that the NTE part # is the same for both 2N508A & 2N527... can anyone explain why the cross reference webpage spits out NTE102 for both of these transistors ??

The 2N508A & 2N527 are both PNP germanium transistors... is this correct ?

 

[Guest]

2n508a specs here
http://www.datasheetarchive.com/semiconductors/specsheet.php?specsheet=119614

2n527 specs are here
http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=119987

If you have problems finding any of these old transistors - I have a contact here in the UK - who has one of those really really old dustry shops with boxes of stuff including old Germanium transistors in boxes all over the floor
www.zyra.org.uk/birkett.htm

 

[jetboatguy]

Thanx uk03878... If I'm having a hard time finding the NTE replacements, I might consider buying a NOS purchase from that shop.

A local repair guy gave me a possible explanation on the cross reference confusion:

"most likely, both numbers share the same essential characteristics..... switching times, HFE, pin-out, etc., but have slightly different maximum allowable voltages and/or currents. The NTE number would have high enough maximums to cover both"

sounds reasonable... ??

 

[jetboatguy]

[quote author="uk03878"]www.zyra.org.uk/birkett.htm[/quote]

does this shop have an email address...?