Re: 450TL on eBay

[k4kyv]

Eimac 450TL Transmitting Tube - 160538737878
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160538737878&ssPageName=STRK:MESELX:IT

"Filament Continuity confirmed.  Some emission spots on the inside of the glass."

And someone would actually pay $50 plus shipping (and that's just the starting bid) for that p.o.s.? 


"Insurance and actual shipping fees are the responsibility of the buyer.
Shipping rate is an example from 77073 to New York City.
Buyer pays actual shipping rate to your location."

Like there's even a slight possibility that it might arrive via Fed-Ups intact? I'd bet it would come with pieces of filament rolling around inside the glass envelope, if the entire plate/grid structure wasn't dangling loose.

[w5omr]

Eimac 450TL Transmitting Tube - 160538737878
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160538737878&ssPageName=STRK:MESELX:IT

"Filament Continuity confirmed.  Some emission spots on the inside of the glass."

And someone would actually pay $50 plus shipping (and that's just the starting bid) for that p.o.s.? 

Well, since *I* was the one that listed it, Don, I know it's not a p.o.s.  I've had the filaments lit on it, even had it in a circuit and it was producing power out.  Perhaps I should have defined it better

"Insurance and actual shipping fees are the responsibility of the buyer.
Shipping rate is an example from 77073 to New York City.
Buyer pays actual shipping rate to your location."

Like there's even a slight possibility that it might arrive via Fed-Ups intact? I'd bet it would come with pieces of filament rolling around inside the glass envelope, if the entire plate/grid structure wasn't dangling loose.

If you had paid attention, the shipping method would have been USPS, -not- UPS, nor FedEx.

I've got another one.  Would you like to make an offer on it, privately, since it seems you're interested in 450TL's?

[KE6DF]

I bought a 6C21 (a very similar tube) on ebay a year ago. It came in good shape.

The guy who sold it did a great packing job.

He used some kind of liquid foam packing material that hardened to a thickness of about four inches around the tube.

I kept the box with the foam as a great place to store the tube.

Dave

[K5WLF]

The liquid foam packing system works great. We built a plywood 'coffin' to ship a 6" Takahashi refractor telescope cross country a while back. We filled it just shy of halfway with liquid foam and covered the foam with a couple of cut-open trash bags, and laid the scope in there, suspended by a couple wires to keep it from sinking all the way into the foam. When the foam set up, we pulled the wires, laid a couple more bags over the 'scope and filled the box with more foam. Once it set, we cut it level with the top of the box and screwed the lid down. It went from Texas to Arizona and back with no damage to the 'scope.

We know the foam packing system works because it went both ways via FedEx and even those folks couldn't break our scope.

ldb

[k4kyv]

Well, since *I* was the one that listed it, Don, I know it's not a p.o.s.  I've had the filaments lit on it, even had it in a circuit and it was producing power out.  Perhaps I should have defined it better

Didn't notice that the seller was someone who would know what he was talking about.   

Geoff, you should have included the above italic quote in your description; that would have made it appear more credible.  As it was, it looked too much like the standard "Sold as is: filaments light up but I have no further means of testing it" ePay disclaimer.

If you had paid attention, the shipping method would have been USPS, -not- UPS, nor FedEx.

I've got another one.  Would you like to make an offer on it, privately, since it seems you're interested in 450TL's?

I traded off my last 450TLs several years ago. Even though I used overkill when packing them including double-boxing and  plenty of bubble wrap, one filament still got smashed in transit.  I think there is something about the filaments in Eimac style tubes (particularly WW2 production) that gets brittle with age, and it doesn't take much to break them.

I don't need any 450TLs, but I am always in the market for HF300-like tubes if I think there is any possibility of getting them here un-destroyed.

I have had extremely poor results with shipped tubes the past few times.  Of the last four HF-300s that were shipped here, three were destroyed in transit, and the one that made it intact was probably the only one of the four that was already beaten to death and had no emission - Murphy in action. Two of the tubes were shipped via USPS, but the seller didn't pack them well.  However, the box arrived with one side caved in and all corners rounded so I doubt they would have made it even if he had packed them properly.  That seller was the ex-owner of a well known vintage electronics store, so I mistakenly assumed he knew what he was doing.

Following the last incident, I have about decided the only way I would consider acquiring any more transmitting tubes from distant locations is when I  can pick them up myself and hand-carry them home, or have someone personally deliver them whom I would trust will take care of them in transit. Large transmitting tubes are getting too scarce to waste the remaining few by allowing the Fed-Ups gorillas to destroy them. I do trust USPS a little more, but they are far from perfect, either.

I wonder if anyone has had any luck using those old Eimac shipping containers that have the tube suspended with springs inside a rigid metal framework.

[W2PFY]

I guess I have better luck shipping large tubes. I have purchased about 10 450TH,TL and 6C21's over the years and none were broken. I even purchased a 750TL and later sold it and it didn't get broken.

450TH and TL's usually bring less than 50 bucks so I won't sell any of mine. When it comes to 250TH tubes and 100TH tubes they always average about 50 percent failures not because of shipping damages. Most of the time, they are gassy.

If you get $50.00 for a 450 tube by the time you list it and pay PayPal, you wonder why you do it? 

[WQ9E]

Don,

It may just be a coincidence but in the last 4 weeks i have received 4 horribly mangled boxes from USPS which previously had caused no problems for me.  All were well packed and at least double boxed but one item (a power supply) still got dented a bit.  More interesting was the solid pieces of styrofoam surrounding the power supply were reduced to confetti so in addition to some solid hits it looks like the package experienced sustained vibration causing the perforated supply cover to act like a cheese grater on the packaging material.

I have received a lot of poorly packaged stuff via UPS that was still intact and I have had very good luck with FedEx.  It looks like I am about to have three fairly rare pre-war receivers shipped here from the southwest and I plan to have the seller use FedEx.

[W2VW]

Ebay sellers are guilty until proven innocent. Part of the fun.

[K5UJ]

Well, I've always been told to never buy any of those long plate structure tubes (the TH and TLs) unless you can get them in person because they are so fragile.   Last year I purchased a few lots of tubes including a number of 4x1 from a ham over in Iowa and for the 4x1s I drove over and got them. 

Rob

[KM1H]

Ive recently purchased 3 NIB 6C21's from the Left Coast and all arrived in fine physical shape. One is a bit gassy for AM on the hi-pot but I havent had time to reconfigure the regettering jig yet, it may be salvagable and if so all 3 will get turns as the odd man out.

Some day I'll find some 750's or larger

Carl

[Todd, KA1KAQ]

I picked up a nice 450 at NEAR-Fest V or VI, still in its suspension frame, for $25. I'm not aware of any rigs in WWII that used them, if so, not many. Therefore the issues seen with the much more prevalent 100 and 250TH/TLs (used in BC-610s and others) caused by wartime quality metals used in the process shouldn't be an issue with the 450 series. My understanding is that the metals used not only caused brittle filaments, they also added to the gassy tube problem by releasing more unwanted materials inside the tube over time.

[k4kyv]

Ive recently purchased 3 NIB 6C21's from the Left Coast and all arrived in fine physical shape. One is a bit gassy for AM on the hi-pot but I havent had time to reconfigure the regettering jig yet, it may be salvagable and if so all 3 will get turns as the odd man out.

Some day I'll find some 750's or larger

Carl

Run your 6C21s at 7.5 volts on the filament.  The 8.2 volts or whatever it is, recommended in the Eimac tube data sheet, was used to increase the peak emission of the tube for radar pulse modulator service, at the expense of tube life. From what I  have heard, the filament in the 6C21 is the same as that in the 450TH/TL.

Just make sure the filament voltage is not low enough to limit peak output, as indicated on a scope.  High filament voltage rapidly shortens tube life, but so does starving the filament with low voltage, enough to clip peaks below normal values.

[Bill, KD0HG]

I traded off my last 450TLs several years ago. Even though I used overkill when packing them including double-boxing and  plenty of bubble wrap, one filament still got smashed in transit.  I think there is something about the filaments in Eimac style tubes (particularly WW2 production) that gets brittle with age, and it doesn't take much to break them.

Haven't had the same problem with 304s. They have a much huskier filament structure.

I've had the same experience with WWII vintage 100-THs. Waaay overpacked during shipment, but still open filaments on receipt. You are probably correct about the filaments becoming brittle with age. Perhaps a s-l-o-o-w raise in filament voltage with a variac would help anneal them before shipment or putting back into service.

[W2PFY]

6C21 HAM SPECS.

[k4kyv]

Thanks Terry for the 6C21 data.

When I ran a 304TL in the final in the mid-60s, my problem was that they would only last a few months before one section would start dissipating less than the other 3.  Then another section would go.  Sometimes the plate on one section would go completely dark, while the others were dissipating the full power and running white hot.  The filament brightness wasn't affected, except for one or two tubes in which the weld between the stranded wire  lead to the tube pin and the solid wire coming out of the glass, failed.

I had about a  half dozen tubes and went through the whole bunch in less than 2 years.  All voltages were correct and tubes had plenty of ventilation, although I didn't have forced air on them (data sheet from Eimac didn't call for any).

When I used up all my 304s, I  rebuilt the final to its present form in push-pull.  Have used 810s, 8000s and HF-300s in the final.

Everybody else I have ever talked to who used 304s said they never had that problem.  I don't know what I was doing wrong.  The tubes came from numerous sources, so they weren't all from the same batch.

I did find that the ones with the metal ring round the glass envelope, and separate grid leads coming out the side welded to the ring, were inevitably gassy.

[Bill, KD0HG]

Don, I've never had that problem with 304s. I have always run forced air on them, a good side blast of air and I don't baby them. I've had only one go bad on me in 15 years, failure was due to getting gassy.

I can't imagine the cause behind the failures you described if the filaments were all lit. Unless one of the four internal grids failed from over dissipation or heating.

[W2PFY]

A minor hijack. I remember when 304's were 25 cents each. Hams at the time pissed & moaned because the filament current was too high and went out and bought a fifty watt job. Another thing I find fond to remember that hams also at the time rated their tubes by the filament wattage, rather than the plate dissipation

I think it goes like this a 50 watt filament tube was good for 500 watts and a 100 watt filament was good for the FULL gallon.

And what the hell does hi diddle bump mean?

[W9GT]

6C21 HAM SPECS.

Thanks for the 6C21 data Terry!  I have a pair of NOS Eimac 6C21s and 2 or 3 used ones.  I am in the planning stages for construction of a new "super" rig using a pair of 6C21s modulated by a pair of 304TL's.  I have mod xfmr and reactor from a Bauer 707.  I would like to find a better plate iron, but I have a "dry" pole pig that will work.  Plan to put it all in an old GE 2-way base station enclosed rack cabinet.

Tnx and 73,  Jack, W9GT

[w5omr]

Thanks for the 6C21 data Terry!  I have a pair of NOS Eimac 6C21s and 2 or 3 used ones.  I am in the planning stages for construction of a new "super" rig using a pair of 6C21s modulated by a pair of 304TL's.  I have mod xfmr and reactor from a Bauer 707.  I would like to find a better plate iron, but I have a "dry" pole pig that will work.  Plan to put it all in an old GE 2-way base station enclosed rack cabinet.

Why not the other way, Jack?  I'd think that a single 304 modulated by a pair of 6C21/450's would provide more than enough audio, provided you've got some sort of multi-match modulation transformer.

Let's look at the Z of the final.  1kV @ 500mA would equal 2000 ohms. (304's are known for high-current)
For the same DC power input, 5kV @ 100mA would equal 50k ohms.  That'd certainly make it harder to provide enough inductance were you to shunt the DC off of the secondary of the modulation transformer by means of a reactor.
You'd need to, depending on the modulation transformer, to pass half an amp of current though the secondary.

As for the modulators, 7500 ohms on a pair of 450TL's at 3kV on the plates for 1400w potential audio.  You could probably get closer to the desired impedance with 2kV instead of 3, and still have -more- than enough oomph to modulate the 500w final.

Of the rigs I've heard/seen/worked/operated, the best sounding has been
a single 833 modulated by a pair,
a pair of 250TH's modulated by (4) 813's in push-pull parallel
a single 5763 modulated by a pair of 12AX7's.

I know of a rig running a pair of 4-250s modulated by 4-125's.  To me, that's just backwards.

[W9GT]

Hi Geoff,

Yes I understand what you are saying and there are all sorts of combinations that will work.  Depends on the components on hand and the "cool" factor that you are after, and perhaps, utilizing an approach that is a little different than the run of the mill.  With the materials I have on hand, I can go a number of ways.  I have a complete push-pull tank circuit set-up, so I was kinda wanting to use that instead of using a single-ended final.  Certainly, one 6C21 would be plenty in the final, but two would be cool, using the old B&W butterfly cap, HDVL coils, and swing-link arrangement.  As for the modulator....well....304TLs will put out a lot of snot!  You can run them over a wide range...and, of course they will put out a lot of power with lower plate voltages.   The Bauer iron that I have is somewhere around 12K primary Z and 8-9K secondary, I think....was used with 4-400As by 4-400As.  The mod reactor is 65H @ 500 MA. Of course you can tweak the values of Plate E & I and come up with many combos that will work.   Anyway....no holes drilled yet...just looking at using what I have to build a super cool rig  

Thanks & 73,  Jack, W9GT

[k4kyv]

The optimum design of a modulator and final is more involved than simply calculating the modulation transformer impedances and turns ratio based on the published impedance properties of the tubes. 

If a common power supply is used for modulator and final, regardless of the impedance level, the modulation transformer needs to have a turns ratio of about 1.4:1, or a 2:1 impedance ratio.  The only case in which a "multi-match" transformer, with a choice of several turns ratios, is useful is when separate supplies are used for modulator and final, and different plate voltages can be applied to the modulator and final tubes.  Otherwise, an appropriate fixed-impedance transformer is satisfactory, and may actually give better performance.

The  reason is simple.  In a class-B or AB circuit, the peak audio voltage capability of each tube is roughly 80% of the DC power supply voltage.  It is very difficult to drive the grid of a tube hard enough to bring the instantaneous plate voltage below about 20% of the DC plate voltage.  One of the reasons is that, to get the tube to conduct to saturation, substantial positive voltage must be applied to the grid, and this peak grid voltage is likely to be close to 20% of the plate voltage.  With a triode tube, it is impossible to bring the plate voltage below the grid voltage, no matter how hard the tube is driven.

With two tubes in push-pull, the total peak a.c. (audio) voltage across the primary of the modulation transformer is the sum of the peak voltages generated by each of the two tubes.  If we assume the figure of 80% of the DC plate voltage, that means that the the total peak audio voltage developed by the modulator tubes cannot exceed 1.6 times the DC plate voltage.  Therefore, for exactly 100% modulation capability, the turns ratio, total primary to secondary, would be approximately 1.6:1, or 2.56:1 impedance ratio.  But to avoid distortion near the 100% modulation point, we need some head-room, so that the tube is not being driven to saturation right at the instant that 100% modulation occurs; therefore it is preferable to have a little less step down, maybe 1.4:1 or 1.5:1.  If you are looking for extended positive peaks,  a ratio of 1.3:1, 1.2:1 or even 1:1 would be necessary.

Where the plate-to-plate impedance comes in, involves how much current is run on the final.  By Ohm's law, modulation impedance = plate voltage/plate current.  This impedance is reflected back to the modulator tubes via the transformer.  So you need to choose a plate current that will give the proper modulating impedance that when reflected back to the modulator tubes through the transformer, will allow the modulator tubes to work into a satisfactory plate-to-plate load.

There is nothing sacred about the p-to-p load recommendations given in the tube charts; they are just that, recommendations. With most good tubes, the p-p load they work into can be varied considerably, maybe as much as 2 to 1 and still get good results.  When working the tubes into a lower p-p load impedance, the peak plate current will be higher, the plate dissipation will increase and the stage may become less efficient.  Taken to extreme, the linearity of the tube may suffer.  But within reason, the main thing to watch for is plate dissipation and maximum peak plate current.  The maximum peak output from the tubes may be reduced when one veers too far from the recommended p-p impedance, but if peak plate current and plate dissipation are kept within the manufacturers ratings, the tube will perform just fine.  The same goes for running at a higher-than-recommended p-p load.  In this case, for 100% modulation capability at the full power rating, the DC plate voltage will be increased.  Again, this causes no problem as long as the maximum plate voltage rating of the tubes is not exceeded.  The tube may run more efficiently at a higher p-p load, but if too much step down is used in the transformer, the peak output capability and therefore modulation capability will be reduced.

The third factor to be considered is the nominal impedance rating of the modulation transformer itself.  This is determined by the amount of iron in the core, the type of  iron used, and the number of turns in each winding. Most good transformers can be run at least +/- 100% of the nominal value, again as long as maximum current and voltage ratings are not exceeded.  If you get too far away from the nominal impedances, frequency response may be affected.  Running a transformer at a  much higher impedance than normal will limit low-frequency response due to the lower inductance of a low impedance winding.  Conversely, running a transformer at a much lower impedance than recommended may limit the high frequency response due to the combination of stray inductances and capacitances in the windings.  Also, the core is more likely to saturate on peaks due to higher currents through the windings. But within reason, the transformer should work OK. 

In fact, this is the principle of operation of the multi-match "universal" modulation transformers.  The same turns  ratios are used for many different sets of impedance walues.  The CVM-5 for example is rated for something like a range of 2000 to 20,000 ohms on both the primary and secondary.  Looking at the charts, you will see the same turns ratio connections repeated over and over to transform widely different impedance levels.

So, getting back to the topic, if a common power supply is to be used, a mod transformer turns ratio of somewhere between 1.2:1 and 1.4:1 should be used, and tube types, DC plate voltage, final amplifier plate current and nominal modulation transformer ratio should be juggled for the best fit. Some compromise may be necessary, regarding both performance and power output, when one is limited to using components on hand.

Calculating the mod xfmr turns ratio based on published modulator impedances and final amplifier plate voltages/currents listed in the tube charts may or may not meet the above criteria.  If not, it is better to push the load and modulating impedances a little beyond the tube chart recommendations, or live with slightly less power output capability, than to veer too far from the optimum the modulation transformer turns ratio as described above when using a common power supply for the modulator and final.