Fisher had tube gear listed as late as 1971?
The logo plate has a strong similarity to the one on my FM-100-C.
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My new Fisher 1800!!
- Thread starter chameloman72
- Start date
Fisher had tube gear listed as late as 1971?
The logo plate has a strong similarity to the one on my FM-100-C.
No, no, I didn't mean to imply that. There are tube receivers in my 68 catalog, I don't have the 69 or 70, and there aren't any in the 71.
It is not possible to nail down the "production" dates for Fisher receivers to a set period of years.
Marketing and engineering were not necessarily in synch, which is the norm for pretty much most companies, then and now.
There are copyright dates on all the catalogs, but those were printed months in advance, and were published/released for some time afterward. Product was manufactured, warehoused, and shipped over a period of time. Specific receivers, when still in stock, continued to be shipped, if available, long after a new catalog was released.
This was the standard procedure, and was, if anything, more prevalent during the transition period between tube and solid state. The 1800 was an 800-C with different cosmetics. The 800-C was listed in the 1968 catalog, and there were no tube receivers listed in the 1971 catalog at all. So, we can safely assume that Fisher was done with tube receivers by that time. Therefore, we can assume that the 1800 was probably in production for a short time between 1968-9 through 1970-1.
Give or take.
Any production date stamps on sub-components such as transformers, on one single piece of equipment, probably wouldn't change those dates.
Marketing and engineering were not necessarily in synch, which is the norm for pretty much most companies, then and now.
There are copyright dates on all the catalogs, but those were printed months in advance, and were published/released for some time afterward. Product was manufactured, warehoused, and shipped over a period of time. Specific receivers, when still in stock, continued to be shipped, if available, long after a new catalog was released.
This was the standard procedure, and was, if anything, more prevalent during the transition period between tube and solid state. The 1800 was an 800-C with different cosmetics. The 800-C was listed in the 1968 catalog, and there were no tube receivers listed in the 1971 catalog at all. So, we can safely assume that Fisher was done with tube receivers by that time. Therefore, we can assume that the 1800 was probably in production for a short time between 1968-9 through 1970-1.
Give or take.
Any production date stamps on sub-components such as transformers, on one single piece of equipment, probably wouldn't change those dates.
Just noticed that this thread was in the wrong forum. Moved to the Fisher Forum.
wa2ise
Super Member
I was confused when changing the coupling caps as they were .047UF, but two of them were rated at 630v and two rated at 400v?? Was someone hitting the bottle when they put those in or what? They definitely were the originals ...
Maybe the 630V ones coupled to the plate side of the phase splitters, and the 400V to the cathode side of those phase splitters? Though I haven't looked to see what Fisher used in that unit.
The general consensus is that it was simply a way to save a few cents. You can safely use all 630v replacements.
I don't like you anymore.Amazing score, those 1800s are really rare! Every Fisher 500C/800C I've ever seen had the .047uF 400 and 630V coupling caps in it. I'd replace them with .1uF 600 or 630V. Get that thing fully restored, and enjoy. You have a Fisher treasure.
It's not electrically necessary to pair up the wV on the output couplers on these. The PI outputs are running at very unequal voltages. The low voltage leg is only 130v. A 400v part is very conservative there.
Besides saving a few cents, the lower wV part provides balanced operating headroom compared with the high side leg. To adherents of dielectric break in and other materials physics theories, it may be audible . . . or may be not.
Don't double the capacitance value unless you are messing with the RC factor (changing grid leak resistor values). The corner frequency on these at stock values is already quite low (@10hz). At stock RC values, it accomplishes nothing but increasing the parts bill and eating up underchassis space.
The 7591A was effectively (during its OEM period) a US-only made output. The original designer was Westinghouse, and they are the best in my opinion. The others are Sylvania and GE. All the old production are very good sounding. You may find any of these in any Fisher product. You need to check the EIA codes to see what you have. Later production instruments are more likely to carry Sylvanias in my experience. The sonic signature among the original makers is close enough that you can get by (if need be) with two different make pairs if you are not too discerning.
The old production 7591A is a surprisingly rugged tube that can handle some abuse. Do not be put off by burned looking ones or dried out base caps. Raising the base bias supply voltage above -19v will dramatically increase their remaining life, and can alleviate the need for a resistor hack with new production ones otherwise prone to red plating.
FWIW, Teles are a safe, clean, excellent sounding tube in many applications, including Fisher receivers. But they are typically renowned in small signal applications in these instruments. You will not find a Tele 7591A; they don't exist. Prior to the C series, you could find any combination of assorted make tubes being used in the small signal sockets. But for a stretch in the mid '60s, Fisher dropped primarily Teles into the X7 positions on these. By the end of the tubed production, Fisher was using lots of different manufacturers (again), and you'll find plenty of Sylvanias in them.
The OP should do an archive search if planning to use other than old production outputs, as new production have some grid leak weaknesses that may necessitate a resistor change. The EH new production 7591A is a good sounding tube, and if they fit, there is nothing wrong with using them.
The 1800 was a '68 model, and was first available sometime in the later part of '67. I believe it and its hen teeth companion to be a one model year run. Although you could buy NIB 400s into the very early '70s for very little at some outlets (well after they were actually produced).
chameloman72
Active Member
I used .047@600v for all of them. Is that acceptable? Thanks
chameloman72
Active Member
All the reading I have done has suggested that the max plate voltage for the 7591 output tube is 550v. So, I would think 600v caps would be fine. I am waiting on my new tubes and then I will check voltages.
Base your output coupling value calculations off of the X7s in the PIs, not the outputs.
The couplers have nothing to do with 7591A plate voltages. The output grid side on these couplers is often running under -20v. You need to add that value to the shield (input) side of the cap to calculate total wV. But most of the wV is coming off the shield side.
The HV input side is running off the X7 PIs. The most you will likely ever see on the high leg (plate) is about 350v. The low leg runs off the cathode, and is substantially lower.
One GOOD reason why the low leg on these is under 150v is that applying 300v+ to an X7 cathode is likely asking too much of it.
I like to apply a 2/3 de-rating factor to main couplers in these, especially when running PIOs. That comes out to 1kV on the high leg and 400V on the low. But with dry films, even 600/250s will work (250 is cutting it close, though).
The important thing is that you want ZERO leakage. Just a few volts leakage is enough to murder an output.
Jailtime
Standin' on a corner
My 800C has the .1uF coupling caps in it, and also the resistor mod to run the new production EH tubes. I'm just going by that unit for recommending parts to change. Nice to know why those values change for new tubes though! :thmbsp:
MouseMaster
Active Member
The 400 I'm going through now is the same way. I put .87 / 630 Sonicaps in mine. That's a nice looking receiver you picked up there. Nice find! And a bargain at that! Enjoy it! :thmbsp:I don't like you anymore.
You'll probably hate me with envy but...
I have a Fisher 1800 receiver that I got for FREE a few months ago...:yes:
I took it out out of this nasty old stereo cabinet that was sitting by the roadside in my neighborhood. The cabinet was moldy and falling apart but the receiver was OK. It works and actually is in fairly nice condition!
I only powered it up a couple times for about 20 -30 minutes. I plan to do a re-cap and cleaning soon. But it sure does sound nice through my Advent Heritage's
I have a Fisher 1800 receiver that I got for FREE a few months ago...:yes:
I took it out out of this nasty old stereo cabinet that was sitting by the roadside in my neighborhood. The cabinet was moldy and falling apart but the receiver was OK. It works and actually is in fairly nice condition!
I only powered it up a couple times for about 20 -30 minutes. I plan to do a re-cap and cleaning soon. But it sure does sound nice through my Advent Heritage's
Congrats on a great find!
Saint Johnny
Bon Ton Roule
x eleventybillion!
The last 1800 I saw on the bay, got pulled less than 12 hours after it went up.