In a complete quandary

[eleventeen]

I have two of these SKL Spencer-Kennedy Labs #300 variable high-low pass filters.
They probably function as well as 5 qty 25 cent TL082 op-amps or any number of parametric EQs





Each one has 5 qty nice Telefunken 12AT7, plus a 5Y3 and a few other non-useful tubes.
A tranny easily usable for a 5E3-flavor amp
nice shielded tube sockets, switch, a Fender-style pilot lamp ass'y, and some very usable pieces of sheet metal for brackets, standoffs, etc;

As they are heavy, I doubt they could sell on ebay for even $35 each, considering freight I would have to charge, and after taking their cut, I could maybe make $20 on them, which is what I paid for each of them. (I have checked)

Bottom line is that they have a lot more value in parts than I could hope to sell them for; but they are so cool, I hate the idea of taking them apart. Yet I know I will never use them for anything. I think I need to find a local tube audio freak and trade for something.   

[Platefire]

Yep. On todays slow market think you would do better parting them out. However you could mark them up on e-bay to a price it may be worth your while and try that first. I think you can re-list up to three times now without being charged extra with it. Platefire

[eleventeen]

Thing is, I have checked what these things go for on ebay, and it is small. A buyer will have to pay minimum $25-30 for incoming freight, each, so that gets added to the landed price. I am thinking I would be better off finding some local tube-addict with whom I could trade these for maybe an integrated stereo amp in as-is condition that would either function as parts bins for two amp builds or possibly be rebuildable. There's no getting around the notion that they are worth more in parts than what they can be sold for, unless I find the true religious zealot.

[TubeGeek]

I'd be interested in trading for or purchasing the 12at7's if your interested.

[BrianS]

I'd like to hear more about the transformers...

[HotBluePlates]

I'd like to hear more about the transformers...

A tranny easily usable for a 5E3-flavor amp

Is it really?

No schematic, so I'm guessing that the smallish black transformer is the power transformer, while the big gray box is the output transformer. The PT then looks much smaller than a 5E3 PT, and while voltages may be similarly-low, very likely has no where near enough B+ current capacity for a pair of 6V6's.

By that I mean you can build a 5E3 using that PT and you'll likely get sound through the speaker, but if current capacity is too low, the B+ will sag severely when pushed and power output would be weak compared to a real 5E3. Then again, maybe that's a good thing if you don't need all the output of the 5E3...

The output transformer has indeterminate primary & secondary impedances, and may be "too good" (have too much bandwidth) for a guitar amp. After all, the original filter was supposed to have response to 200kHz if you didn't roll it off with the filter.

Each one has 5 qty nice Telefunken 12AT7, plus a 5Y3 and a few other non-useful tubes.

The "non-useful tubes" look to be part of the regulated power supply for this filter. They'd be good as part of another regulated power supply (maybe one exactly like what's already in this, with the same PT and output B+ voltage & current).

The series pass tube might be useful in pairs for a push-pull output stage, if you're willing to do the design work to figure out how to use them. I'm betting plate & screen voltages would need to be lower than you're used to in guitar amps.

[eleventeen]

Entirely valid point on B+ ampacity HBP. Strictly a "size" eyeballing exercise. I generally consider that if I go to a SS rectifier and lose 10 watts (5 volts, 2 amps) of demand from the 5Y3, I can overtax the B+ just a little.

I would expect the output tranny (and I have not looked at it) to be a 600 ohm output impedance so I had no expectation of being able to use it for much, if anything.

You bring up an excellent point (as to the pass element) which I have started to investigate and gotten...only so far.

The pass element in the reg power supply is a 6AV5, which is similar to a 6AU5. These are hefty tubes which appear to be more capable of passing current than 6V6's. They are actually close to 6L6. They're like 7591's in that (and only that) respect.

These tubes are available really cheap, in NOS.

One thing I have found out is that the screens want to be operated WAAAAAY below the plates. Not 5 volts lower, hundred(s) of volts lower. 

Incidentally, another tube which would be great to use as an output tube is a 6W6. Rugged tank of a tube, heavy filament current in a 6V6-sized bottle. Run HOTTT.

I've checked in a few audio forums as to the utility of 6AU5/6AV5. I am only midway through that exercise.


 

[HotBluePlates]

I would look into the utility of the pass tubes, but I currently have equipment which uses them, so I'm more likely a buyer for replacement rather than re-purposing. But you never know...

I agree though that the best use of these filters is passing along to some other tube nut that will prize them. Not sure who that might be though.