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Pitiful X-202

Frannie -- You go girl, and get your 202 runnin'! It is worth the effort.

Without a doubt high power designs can get complicated real quick, as can ultra low distortion designs (high NFB levels). To my mind, NFB is not a bad thing at all, but used to excess, can tend to suck the life right out of the music. By comparison then, smaller, lower powered, lower damping factor designs like your VM "thing" (:)) can add a realness that is compelling for sure. The trick has always been to hit that elusive target of accuracy, with realism.

Dave
 
Walyfd -- Back on topic now, the loudness control is very definitely volume setting sensitive, with the greatest effect by far happening below about 11:30. That is by design as the assumption was that operating the unit any higher setting than that would produce such a sound level that the original intention of the loudness control effect would not be needed. Therefore, it intentionally has no effect above about a 12:00 setting.

The Rumble and Scratch filters are electronically completely separate from the loudness function and volume control, but will effectively interact with those controls due not only to the way our ears perceive sound, but also because they are filters that are basically in series with each other. For example, if you have the Rumble filter on, and the volume control is within range, the loudness switch will boost and cut bass frequencies, based on it's setting. However, given sufficient program material, turning the Rumble filter off in this scenario will cause the loudness switch to apparently boost (and/or cut) the low frequencies much more -- because there are more frequencies for it to react with when the Rumble filter is turned off. A similar effect happens with the Scratch filter/Loudness switch as well, since the loudness switch boosts both high and low frequencies when activated.

Dave
 
Precisely what I've noticed. I generally have the Loudness Contour "on". I don't use the filters, though. With both the 202 and 500, I thought the rumble filter would magically compensate for turntable deficiencies, but I was WRONG! There's just so much the filter can really filter. That's what got me into rebuilding the Garrards.

The filters work differently with tape recorders than phonographs. There seems to be more filtering.
 
One other thing I would also mention about the 202, is that it does invert the absolute phase from all inputs except the Tape Monitor input.

Some are sensitive to this issue, as it does represent a deviation from the original recorded material.

If the issue concerns you, the easiest answer is to reverse the connections to BOTH speakers, which will reverse the phase of the signal presented to them, and restore absolute phase integrity. Of course, then the absolute phase will be inverted for signals presented to the Tape Monitor inputs. Therefore, in installations where all of these inputs are used, a switch in the speaker leads to reverse the phase to both speakers (depending on the input used) would be the best of all worlds.

I pulled on this thread in the X-1000 project which has similar concerns, ultimately correcting the problem internally with the new design of the control section for that unit. However, I have sworn off of such efforts with this unit. Since I tend to only use one high level input, my answer will be to just reverse the leads to both speakers.

Dave
 
dcgillespie said:
One thing I keep meaning to add, concerns the front panel "Rumble" and "Scratch" filter switches on the X-202.

These names imply that these switches only operate with and impact sound produced from phono inputs, since the terms rumble and scratch are descriptors associated with producing sound from playing records.

In the design of the 202 however, these switches are really the electronic origin of what became known on so many later units as "Low Filter" and High Filter" -- be it receiver or straight amplifier oriented. Specifically, I don't know of any design predating the 202, that includes such filters, designed into the circuit in the manner that they are in the 202.

The X-101ST certainly predates the 202 (being the first stereo integrated amplifier Fisher produced that I am aware of), and does include a Rumble Filter switch. But that switch in that design is decidedly connected to and operates only with the phono preamp circuits. In the X-202, the Rumble and (new) Scratch filter switches operate (for the first time) in the line amplifier stages, meaning that in spite of their designated titles, their operation actually affects the sound from any and all inputs.

It is strange then that Fisher would give these switches the designators they did on the X-202. But these were fast changing times during the early stereo days of 1960. The electronic aspect of how these filters function was certainly changing, but the descriptors they were given apparently lagged behind their changing operation. The X-202 went through all of its own iterations with these switches always labeled as Scratch and Rumble. Only with the introduction of the X-202B did these (basically electronically identical) filter functions finally become known as the more generic Low and High filter switches.

In any event, for those who have these amplifiers, just be aware that these switches will in fact affect the sound on all inputs playing through the X-202, so make sure they are set according to your preferences!

Dave
Click to expand...

Thanks for this information!
 
Dave, I just ran across this thread and was wondering about the use of EFB in this amp, was this something you did or contemplated? I have coming an X-202 that may be mere typified as a "rat rig" and would be looking to use your ideas as a template for bring the X-202 back to life and use as a daily driver. Thanks, Randy
 
I did not include it in my X-202, as I wanted it to largely remain a reference piece against which modifications can be measured or judged.

If you are interested in adding EFB(tm) to your X-202, search for the thread "Improving the Fisher SA-100 with EFB II". Since the power amplifier section of the X-202 is basically an SA-100, the process would be nearly identical.

Dave
 
thanks, Dave, I will give that a study to see how to incorporate that into the beater when it gets here and I start up the project.
 
Dave:

RE: "...A decent set of Russian military tubes fill the output tube sockets..."

Q1: which Russian tubes specifically did you use, or which would recommend please?

I have a rebuilt X202 that I just bought without output tubes, and I'm currently looking for the best-bang-for-the-buck choice in output tubes

NOS vintage 7189s are getting kind of expensive and hard to find, so I'd like to consider alternates -- but only if they sound as good and are up to the task durability-wise

Q2: also, how important is it to have matched pairs in each channel?

thanks!

PS: very interesting thread here and nice work... my X202 is also pretty beat up looking, but I kinda like it that way... looks battle worn and it really adds a lot of character for sure
 
That (Sovtek EL-84M) or the Russian 6p14p-ev (also known as 6n14n-eb). The 6p14p-ev is getting harder to find tho as stocks are starting to dwindle, with an associated price increase. The New Tung-Sol EL-84 Re-Issue is supposed to be able to handle hard running fisher's, Scott's, etc., according to their Co. Info. And McShane is hearing positive comments on it also.

But any tube that you do end up getting needs to be load matched at operating voltages, not just emissions and gm on a tube tester. Which is what 99.99999940% of E-prey sellers and a lot of commercial sellers do. Jim McShane tests at operating voltages and loads, and you get load matched (to within 1%-2%) tubes. Jesse Brent is also good for testing in real world conditions.
 
The tubes installed are in fact EL84M tubes. They operate very well in the 202, allow it to produce full rated power output, and have been holding up quite well also. At last check (about 1675 hours), they were all still producing > 96% of their new power output productions figures. They also sound great, with all the dynamic energy that the 202 is so noted for!

Dave
 
so are these Russian EL84M tubes current production, or vintage?

would vintage 7189s (US-made or otherwise) have any benefit over these Russians, other than the authenticity and perhaps some "coolness" factor... ie., would they sound any better or be more robust?

thanks
 
Regarding the sound of different tubes, everybody has their own opinion. For me, in this design, I serious doubt that there is any "real" difference in sound between any of the good tubes available. Expectation bias is a powerful thing, so any real sonic signature of various tubes should only be determined under strict double blind testing conditions. To my knowledge, the EL84M is a vintage tube that is no longer produced. I am also using a matched quad of the new Gold Lion N709/EL84 tubes in my SA-100 clone, and have had excellent performance out of them as well.

Dave

Edit: I see that (thanks to Larry) Jim McShane is indicating that the EL84M is a "current production" tube. Nice to know!
 
Dave; Sovtek has a EL-84M out that is the current descendent of the 6P14P-EB according to McShane. And they are fairly inexpensive. What I'm running in the R-20 amp, and TA-600 now. Fantastic sounding tube. Gotta get some more for the 510 & 610, and the 30A in the 560. The TA-600 is running the plates @ 395v (370 spec) on 123V with no problems.
 
RE: "But any tube that you do end up getting needs to be load matched at operating voltages, not just emissions and gm on a tube tester. Which is what 99.99999940% of E-prey sellers and a lot of commercial sellers do. Jim McShane tests at operating voltages and loads, and you get load matched (to within 1%-2%) tubes. Jesse Brent is also good for testing in real world conditions."

I'm trying to get a better understanding of just how critical this is, ie., proper, close load matching between tube pairs in each channel

seems to me that in the old days, someone would have an output tube die, then just walk up to the local cigar store and buy a single replacement (for a few bucks!), then go home and stick in in and all was good

or wasn't it?... is it really that risky for the amp's health and/or the sound quality?

I'm wondering because I'd really like to stick some nice vintage tubes in my Fisher X-202, but it's going to be a LOT harder to find a correctly load-matched pair, let alone 2 pairs like that (of the same tube manufacturer and type)

also, if one just buys random tubes that are only "tester matched", how far off are they typically vs. load-matched tubes?
 
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RE: "Dave what are you using for a 12AX7 in the tone control socket in you X-202?"

I'm also interested in this particular tube position in my X-202... in layman's terms, what role does this tube play and how much does it affect the sound of my X-202?

asking because I have a really nice single Telefunken that I could stick in here, but don't want to waste it if not necessary
 
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SS -- Depending on the circuit, output tube matching is important not only to produce minimum distortion, but also to keep ALL of the output tubes within a safe heat dissipation level as well. While you will typically never hear the difference between a matched and unmatched set of tubes from the standpoint of distortion reduction, you certainly will hear the difference between tubes that are reasonably "sharing the load", and ones that are so mismatched as to cause one to operate in a continual red-plate condition, while the other loafs along. Commercial tube testers were never designed with the idea of output tube matching in mind and so, do a rather poor job of indicating any meaningful match. During the test, they make a device under test (DUT) do so little work that only the worst of the worst tubes will test as bad. Sort of like testing the strength of concrete by shooting rubber bands at it. And, the test conditions are so far from real world conditions that any match that might be indicated has no relevance to real use.

Now your X-202 has three chassis mount controls in each channel to make the need for precisely matched output tubes much less important/critical. In being able to adjust the AC Bal (Phase Inverter control), Bias, and DC Balance controls, the differences between most output tubes installed can be minimized. But from an absolute standpoint, it does not provide perfect compensation. Adjusting the controls changes a variety of circuit parameters, so the further away the controls need to be adjusted from theoretical ideal (due to the use of output tubes of greater and greater mismatch), the less perfect the resulting "compensated match" is. Therefore, even when such controls are provided (which always will be with the best designs), there is still great benefit in using a tightly matched set of output tubes. It means that when the controls are then "slightly tweaked" for optimum performance, all circuit parameters will be at or very near optimum, which will always make for better resulting performance, over that produced by the use of largely imbalanced tubes, with the circuit needing to be well contorted so as to accommodate them.

In my own 202, I'm using some very good original Fisher Telefunken tubes in the tone control positions. But please understand: All good designs employ compensation within the design so as to make the differences produced from different tubes in the small signal positions extremely small. Tested under proper double blind testing conditions, you would be extremely hard pressed to hear any audible difference produced between a variety of any good tubes you might try out in the small signal positions of your amplifier. Only the most gross differences (new, versus extremely bad) might be heard, and even that would largely be perceived as simply a change in sound level. Understand that testing for sonic differences between tubes under ANY other conditions introduces "expectation"bias: I've changed tubes, so I MUST have changed the sound. It is a powerful influence that is very hard to overcome. Only when you have NO idea of what tube or component change has been made, but can consistently identify a particular component scenario used SOLELY by some intrinsic sonic characteristic, can a valid component/sonic relationship be made. Anything else is just emotion or bias expectation.

Understand that I am hardly trying to sucker punch the idea of tube rolling, which can be great fun. But do understand that without any controlled test conditions in place, any results will be largely emotional in nature, which besides sound, also includes anything from how much you paid, to how a component looks when installed -- which can also be hugely influential as well!

I hope this helps!

Dave
 
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