Over this last year, I've been stripping out the parts from two very old Tektronics oscilloscopes I found sitting outside in a junkyard -- types 544 and 585A. Aside from spending 15 to 20 years exposed to midwestern storms, snow and cold, there were some missing and bent case parts, bad CRTs, corrosion of switches and sockets, and rusty screws throughout. But the bulk of the small parts were sound, although I haven't had the tubes tested.
As a fun project, I would like to honor the legacy of these 'scopes by building a couple of audio amps from their parts. The power transformers still work, as do nearly all the diodes. The carbon comp resistors have all drifted (if they ever were in tolerance), but there are plenty of CCs to bundle as needed to make up the correct resistances. The multi-section electrolytics will need to be reformed, checked for leakage or replaced, but the small caps (film types or ceramic) are still good.
My goal is to reuse actual parts as much as possible and to repurpose some of the "Tek blue" sheet aluminum, potentiometers, black and red knobs and binding posts to make the overall look and feel remain "Tektronics." The pots are linear and not audio taper, and few capacitors fall into the range we usually use for coupling, decoupling or cathode bypass, so this could become quite a challenge.
There were a few transistors, and I'm trying to identify them aside from Tek part numbers. The references I've found indicate low-power, small-signal use or switching use in current applications. Any power transistors are one of a kind and not in pairs. As a result, I'm not actively including transistors in this project.
I could use some suggestions for the amp tube complement and topology. Here are the more usable tubes for audio that I have on hand from these 'scopes (albeit untested and likely far from matched). The quantity of tubes pulled is in parentheses:
There are also 6EW6 (2) and 6CY5 (2), which I'm not sure are used in audio applications.
There are no output transformers, so to plan to add them would stretch the notion of using only the parts found. An OTL is a possibility if I decide to stay strict, but I'd like to be able to hook up speakers, too, so I may relax that parameter and allow some OPTs.
The power transformers offer plenty of current for heaters, but the highest voltage secondaries available are in the range of 140 to 228 Volts. There are about three high voltage, center tapped secondaries on each power transformer, and they are all different voltages, but they fall into that range. I don't know the current rating for any of the windings, but in some manner they did drive the tubes listed.
The diodes range from the old top-hat metal style to tiny glass germaniums with a few low-volt zeners thrown in. There are a few 2kV to 4kV ceramic caps that could be used as snubbers on the old diodes used for rectification. There are several wirewound power resistors and several precision resistors, with a few of those forming pretty good matched pairs, although the value may not be what's required -- but then some finagling is bound to be needed.
What are your thoughts on some tube combinations or topologies? Since the tubes are used and unmatched, whatever comes of this will be imperfect; it should at least work to some extent, but absolute current balance and channel matching with parts on hand is unlikely. Links to existing schematics are welcome!
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Topic - Any ideas for audio amps from old Tek 'scopes? - jyourison 17:28:52 05/27/10 (22)
- RE: Any ideas for audio amps from old Tek 'scopes? - TimFox 07:42:57 05/30/10 (1)
- RE: Any ideas for audio amps from old Tek 'scopes? - Al Noakes 02:57:17 05/31/10 (0)
- How old are you??? - drlowmu 15:29:04 05/28/10 (1)
- RE: How old are you??? - jyourison 17:15:16 05/28/10 (0)
- I think you are wasting your time using most of the old... - Allen Wright 11:14:51 05/28/10 (9)
- RE: I think you are wasting your time using most of the old... - Michael Samra 12:26:56 05/28/10 (0)
- RE: I think you are wasting your time using most of the old... - jyourison 11:56:23 05/28/10 (7)
- My point of view is that it's... - Allen Wright 16:46:44 05/28/10 (5)
- RE: My point of view is that it's... - jyourison 17:39:09 05/28/10 (4)
- RE: My point of view is that it's... - dave slagle 14:01:10 05/29/10 (2)
- RE: My point of view is that it's... - jyourison 16:22:00 05/30/10 (1)
- RE: My point of view is that it's... - dave slagle 18:32:13 05/30/10 (0)
- If you are ever in Basel (Switzerland) you must visit - Allen Wright 03:40:35 05/29/10 (0)
- wasting your time - richardl 14:53:22 05/28/10 (0)
- I toyed with such madness in my YOUTH! - grhughes 11:02:22 05/28/10 (2)
- RE: I toyed with such madness in my YOUTH! - jyourison 11:46:54 05/28/10 (1)
- The tube power supply is worthy of keeping. - grhughes 17:36:41 05/28/10 (0)
- RE: Any ideas for audio amps from old Tek 'scopes? - JoshK 06:31:10 05/28/10 (1)
- RE: Any ideas for audio amps from old Tek 'scopes? - jyourison 07:39:02 05/28/10 (0)
- RE: Any ideas for audio amps from old Tek 'scopes? - JimL 21:35:03 05/27/10 (0)
- RE: Any ideas for audio amps from old Tek 'scopes? - coffee-phil 18:42:14 05/27/10 (1)
- RE: Any ideas for audio amps from old Tek 'scopes? - jyourison 05:39:28 05/28/10 (0)