Tony, I just realized what I have done- wrong: I rebuilt my Hallicrafters sx-42 painstakingly slow and methodically. But when I got it all done bench checked out and aligned as best I could do. As you know it’s a lot of work- I replaced all the film caps and picked off all the out of spec resistors I could find. The last thing I did before firing it up on it s new shelf next to it age appropriate speaker was change from glass to nos metal 6v6’s. Before it even settled in after turning it on it went into a shreaking oscillation. I turned it off and walked away for a few months. Over time I thought through each step along the way. Long story short the case of one of the output tubes connects at pin 6 and in my sx-42 with glass tubes specified use the pin to connect a bunch of stuff to b+. Lucky I never touched it while on. My sx-42 was built exactly according to one of schematics readily available on line so I got lucky that way. But this simple mistake caused a whole bunch of stressed parts and dead end investigations I probably learned a lot more and watched your videos on the halli regularly for months trying to find out what I’d done wrong. It is a really convoluted design and the layout really isn’t a techs friendly one. I am still working my way back to square one post rebuild but would have ever even thought to do this project let alone get through it with good results without your work to learn from. Thanks so much. It is a really beautiful radio to have and enjoy. David

brad sent me over here, im 3 minutes in and im glad he suggested your channel. this is what i enjoy learning about and you have a huge catalog of videos i can watch...... anyways thanks for you time and patience in uploading to youtube... ill be posting on your older videos and staying up to datewith newer ones. after this ill be checking out x-ray tube part one..... have a nice day tony!!!!

Excellent video Tony but then again I might be biased... :)

Love your valve videos Tony. This is coming from a 40+ yr guitarist. : )

Thanks Tony, another great video.

Excellent explanations Tony. Thanks sharing for your time and knowledge.

Appreciate your in-depth approach to the bias circuit in the amp's finals. Comparing what you found in the amp to the schematic. The original Fisher bias circuit seemed innovative and effective too bad we can't order brand-new American-made tubes. We can't hold the Fisher engineer responsible for the increase in power Co's voltages. Thanks for the instructive video detailing the importance of proper biasing.

If I remember correctly, the 5881, AKA 6L6WGB, is rated at 430 V and maximum plate dissipation of 22 W. Original Tung-Sol 5881 tubes from way back when, however, are very tough and were often operated at well above those ratings ( see the tweed Fender Bassman). I wouldn't necessarily bet that the newer Russian or Chinese substitutes would be as reliable when pushed hard. These days, the Tung-Sol name is just that, a name, owned by New Sensor who also own the Sovtek and Electro-Harmonix brands.

Deja Vu .. I read that book 40+ years ago, and remember it like yesterday (I.e “gumption trap”) .. haven’t heard that book mentioned for decades. However, one of my mechanic KZread authors mentioned it just a few days ago, when he was repairing a motorcycle ...

Big congrats on the new family member!

Another nifty exploration in tube operation.

Tubes give an even order harmonic distortion. This is the appeal of guitarists and audiophiles.

Hi there! A couple of things worth noting... on the EL34's, they draw more current on the filaments than a 5881 or a 6L6, the EL34's draw 1500mA per tube, while the 5881/6L6 draws 900mA per tube. That being said, your EL34's may have some voltage sag across the filaments, especially if the stock power transformer is being used. This potential of extra voltage drop or "sag" CAN cause the distortion that you are seeing on your scope. What you could do is put in the EL34's in and check for voltage drop across them, and compare that VS. the 5881/6L6 tubes. Another tube you can try that may work well is a 7027A tube. It is similar to the 6L6GC, but it can take higher plate voltages (up to 600V) and therefore can dissipate more power (35W max VS. 30W max for a 6L6GC). However, on a 7027A, pin 6 is connected to pin 5, so you'd have to make sure nothing is connected to pin 6 on your tube sockets, otherwise you might have a problem if you try to use 7027A tubes. Also, another tube to try is the Sovtek 6L6WXT+. These tubes are very rugged and I have personally seen these tubes take up to 25% over their maximum rated plate voltage with no fuss. Love the videos, keep up the good work!! Subscribed!

@xraytonyb

3 жыл бұрын

Never thought about the filament current of the output tubes. Although they are not associated with the bias circuit, maybe the power transformer begins to saturate a bit, due to the overall current draw through the transformer? I agree that an 8417 or 7027 would probably be a drop-in replacement for these. I tried a 6550, but that was a bit overkill and the bias was not right for those either, even though they didn't care about the plate dissipation. They also looked really out of place, crammed together on that small area of the chassis! Thanks for the comment!

@ExitThirteen

3 жыл бұрын

@@xraytonyb Anytime! The 6550's suffer the same problem as the EL34's, the filaments are rated at 1500mA per tube, and the 8417's are 1600mA per tube. I have a guitar amp that normally runs a pair of 6L6GC's, but I swapped in a 7027A's and it sounds fantastic while gaining a little extra output (10W). Like you, I was just experimenting, looking into alternative tubes I could install with minimal modifications. I believe J/J Tubes makes a 7027A that is currently in production, although I have had good luck on the Evil-Bay getting the RCA made 7027A's from the 60's and 70's.

Tony, I think you prefer tube sound, even though the measured distortion may be twice that of transistor sound, because you like the sound of 2% even order harmonic distortion, more than 0.5% odd order harmonic distortion produced by transistor amps.

Careful with language when talking to newbies. Nothing 'dissipates current' here. I know its a small thing, just people get these things in their heads.

@1683clifton

3 жыл бұрын

sry beets of the brain.

The 6CA7 is a beampower tube....EL34 is a penthode.....Both are more or less equivalent ....a lot of EL 34 are labelled 6CA7/EL34 ....... The 6CA7 GE often called the Fat Boy is a very good sounding tube.....just like a 6V6G and a 6L6G...... The EL 34 has a 25 watt plate dissipation......The 6L6GC has 30 Watt ....a 7027A has 35 watt .......as has a 7581A..... BUT.....the EL 34 can handle up to 800 volt on the anode......and one push pull of these tubes can be used for a 100 watt output amplifier ....NEVER TRY THIS WITH NEW PRODUCED TUBES , only good NOS tubes can handle these specification... Tubes are inherently more linear devices than solid state semi conductors......and that is one their qualities........also they are less prone to thermal modulation....and need less FB and other tricks to fake exceptional specifications on the test bench.... bass is only limited by the use of OPT's who can only pass AC signals and no DC , even when these OPT's are not perfect or neutral they have other advantages (MC knows that and uses OPT in their Solid State amplifiers)....all those and many other technical characteristics can make a good tube amplifier sing like no their solid state can , how good ial signals measure on sine waves , which are not music but repeated test signals and not dynamic musical signals which are not related to real music transients..with all their harmonics in the right place in time ....FB which lacks real time correction does a mess to the timing of these and the sound ( music ) collapses as they pass a certain level of given FB....but you get a clean lifeless sounding amplifier which measures exceptional on he test bench. It is easy to correct repeated signals......But to correct transients in real time.....That's real life....and Where the vacuum tubes rule. Ever wonder why two amplifiers both measuring 0,005 % THD sound so different and sometimes don't sound good at all ????........ Semi conductors how good they may be are still SEMI CONDUCTORS ..tube are not ! they work at the speed of electrons in a vacuum.... and they are high impedance loading n their command grids. The ear is very sensitive to transients ( time related) .....less on frequency variations...

@BruceNitroxpro

3 жыл бұрын

I agree completely. From stem to stern, as they say. I am knowingly making this statement with a LOT of experience and knowledge of the subject matter. de KQ2E

Excellent !!

I have an ampflier with three 3-500z tubes. It certainly warms the shack just with the filaments lit. Now that’s serious RF Output Power!!

@xraytonyb

3 жыл бұрын

...with the added benefit of being able to roast hot dogs while making a QSO! ;) Thanks for the comment!

@Aswaguespack

3 жыл бұрын

Yep S’more QSO’s for me

If the chassis is at minus 37 volts potential, I would expect that the potential for ground loops and eddy- current noise would be high. I also presume that all the input jacks and such have to be lifted and isolated from the chassis.

Hi new subscriber, really enjoy your channel. Brad the Guitologist sent me.

@xraytonyb

3 жыл бұрын

Thanks for the sub!

How many of your viewers will catch the motorcycle maintenance reference? You and I are getting old. Ha!

would a thermistor help smoothe out the voltage and slow down the current going to the output transformer?

Than you for nice piece of information and knowledge . I do not think there is any mystery in tubes. My idea to the reason of different sounding is placed not in tubes but in speakers. Even order harmonics play role only in overpowering which is not case of HI FI audio but only in El. guitar distortion. In speakers are rooted three kinds of resonances - mechanical produced by enclosure, suspension and membrane, electrical made by connections and band pass filters (if any) and acoustic provided by membrane radiation. The last make no differences between solid and tubes. . Every separate resonance of two first has reflection in phase shifting . Resonance is equity to phase shift. and exists between voltage and current on output terminals - no need to be explained,. It means they do not balance that signal which is coming-in at input. where we compare them by feedback and want not to impact sound . How much it falsely modifies original sound depends on how deep is feedback. And that is main difference between solid and tube transistor.

Good ending words, thanks. Boy what a mine field with all those tube variants.

@2:54 you say that you used a 5W zener in your modification. The 6.3V zener was a 5W but @48:30 in your video about this very modification you tell us that the zeners in parallel with the three fillaments are 1W zeners which I suspect will fry rapidly at the point of the open circuit. It will be carrying 150mA at 12V. Did you "miss speak" about the 1W or did you confuse the diodes as you explained it here? Either way it's confusing.

i think my single-ended Magnavox sounded much smoother than an Electrophonic modular system made 13 years later

I miss my 500; glad to see others love them too. Q.: is there any source for good new 7591 tubes?

@Daniel-sk6ix

Жыл бұрын

oops, meant to say 7581A

@solodolo6018

11 ай бұрын

There's some Tung-Sol ones on Tube Depot for 35 bucks. I've ordered from them before amd recomened them 👍

Sold my collection of hi-end European valves 10 years ago. Siemens, Telefunken, Mullard and some obscures.......Brimar? Made a tidy profit. Interesting to note that 90% of the buyers were from Asian countries. Were they trying to copy?

@xraytonyb

3 жыл бұрын

Don't quote me on this, but I think there has been a huge interest in high-end valve audio in the Asian market. High-end audio in general seems to be very popular over there.

Bit OT, but I'm still curious about that multiplex output jack, on top of the chassis. If it was for an outboard FM-stereo decoder, how would that work on a mono amp?

@Dangrdav

3 жыл бұрын

Fisher made a stand alone mpx-100 and mpx-200 they would plug in. I have been looking for one.

@xraytonyb

3 жыл бұрын

Stereo was a new thing at the time. Very few stations broadcast in stereo, but everyine knew that it was going in that direction. The MPX jack was just an easy upgrade path for the older mono designs. You could just buy an add-on module that would decode the multiplex signal from the tuner and output the two channels. To hear it, you would either need to plug the MPX module into a stereo amp, or add another mono amp and listen to one channel in the built-in amp and the other channel in the additional mono amp. Messy, but it would let you hear the stereo. Thanks for the comment!

is crossover distortion what what happens between upper and lower waveforms

@xraytonyb

3 жыл бұрын

When an amplifier is designed in a push-pull configuration, one tube handles the positive-going half-cycle of the waveform and the other tube handles the negative-going half-cycle. The point at which the waveform switches from positive-going to negative-going is sometimes called the zero-crossing or "crossover" point. In a properly designed push-pull amp, the one tube will "hand off" the signal to the other tube before it stops conducting (at least in a class AB configuration, but that's another subject). If one tube stops conducting BEFORE the other tube starts, there will be a period of zero-signal. It usually shows up as a little notch in the center of the waveform, when looking at a sine wave. This is what we were seeing, when I was talking about the crossover distortion. Thanks for watching!

What about the kt77 is it the same as a kt66 but more output Best have a switch mode power supply for valve amplifiers running at 120kHz much superior What is the best switch mode power supplies medical

@goodun2974

3 жыл бұрын

KT66 is essentially a 6L6; KT77 = EL34/6CA7, and KT88 is pretty much the same as a 6550.

all to do with plate dissipation anode voltage

I didn't know you could even get 910 ohm resistors anymore

what do you think about tube amps that pretty much give a shit and bias themselves? to me that sounds like some sky net type of shit! new viewer from brad guitologist.

@xraytonyb

3 жыл бұрын

I don't have a lot of experience working with the auto-bias circuits out there. They can be pretty complicated with servo circuits and other means to maintain the bias. A lot of those amps will also use an ultra-linear design, with screen taps on the output transformer, but not always. Most of the examples of these types of tube amps I've heard sounded very clean and accurate, very much like a solid state amp. When it comes to tube amps, I like all the "flaws" that goes along with the older designs, but that's just a personal preference. I really like both my Fisher x-101-c as well as my Pioneer SA-9800. Even though they sound very different, they each bring a unique and pleasant sound quality to my ears that the other can't. Thanks for the comment!

@1683clifton

3 жыл бұрын

Way more than I could hope for in a direct answer. I pray you well sir.

how about a 935 ohm resistor

How about running them the way they were....

All Tubes mat...... oh never mind

did a russian company buy the name rights to Mullard?

The zener diode is not good in the cathode circuit, it is too noisy.

@jdmccorful

3 жыл бұрын

How so? Then what would be better?

@RobertZovko

3 жыл бұрын

@@jdmccorful led or ir led

Here is the schematic of 6 op-amp ic tone control with Mid, Bass and Treble Link www.circuitlib.com/index.php/projects/product/84-stereo-tone-control/category_pathway-29. Is it worth building this tone control I would like to know.

8417

@goodun2974

3 жыл бұрын

Vintage 8417 tubes are rare and expensive. Does anybody make a reliable modern version with the same characteristics as the original? I tend to doubt it. Same problem with the 7027 tube....

@Gordonseries385

3 жыл бұрын

@@goodun2974 a close version a modern horizontal tube glass base with anode on top they also used it rf amps forgot the number