Check my work: Ranger to use EL34's.

[KC2TAU]

I have a few spare sets of EL34's and from looking at the spec sheets it looks like I need to tie pin 1 to pin 8 in order to tie the grid together with the cathode. In addition to this I'll also need to raise the modulator bias to ~75-90ma. Let me know if there is anything else I need to do.

[Pete, WA2CWA]

EL-34's are used in the Apache. Look at that schematic and get a feel for anything else you might need to do.

[WD5JKO]

There are many versions of the EL-34. I like the E34L by Teslovak (can buy from Penta Labs) as it has a 30w Pd with a tri-metal plate like a 6L6GC. With these tubes with the plate connection down below you have the pin 3 problem. By that I mean the plate is pin 3 where the spacing for high voltage is marginal. Pin 2 is filament, and pin 4 is G2. Consider a ceramic socket.

I once used 8417's in a Viking I, and I went through pin 3 hell from flaming out sockets. I never did it, but my next step was to saw off the socket around Pin 3, like removing a piece of pie, and use a double heatshrink insulated pin 3 pin in air.

I'm not sure what the Ranger B+ is, but pick an idling current at or below the tube Pd rating of 25 watts. That means 40ma per tube (max) if the B+ is 600v. If you go too low in idle current with any high Gm tube, the distortion products rise significantly. The ordinary EL-34 will have a red spot on the plate at 25W Pd whereas the Teslovak E34L has no color up to 35W.

http://www.pentalaboratories.com/Product.aspx?dept_id=1516&pf_id=e34ls%20mp

Jim
WD5JKO

[KC2TAU]

I'm switching back and forth between the schematic of the TX-1 and the Ranger and it all seems the same except for pin 1 and 8 being tied together. Nothing seems to be connected to pin 1 on the Ranger. I'm just asking just for confirmation as the voltages dealt with in these circuits would cause a mighty large problem if you made an "oops".

Why would the pin spacing be a problem if it isn't already? I'm not going to be running any more B+. The pin out is exactly the same as the 6L6 besides pin 1 and 8. The TX-1 uses EL34's with 750V on the plates and I haven't heard of any issues with pin spacing,either. The Ranger B+ to the modulators is 500V.

[WD5JKO]

Ok, with only 500v B+ the pin three problem is no big deal. Go to +750 and watch out!

Yes a jumper from pin 1-8 is necessary to tie g3 to the cathode, just like other tubes do internally like the 6L6. I'd caution you though, that maybe pin 1 is used already as a connection point at the socket since with 6L6/7027 pin one is not connected to the tube internally.

Looking at RCA data for 6CA7/EL34, class Ab1 audio P-P they idle the tubes (pair) at 120ma with 450v B+ !! 450X.06= 27W when the MAX Pd rating is 25W. They still had 5.1% THD. The 6L6GC/7027 will give you slightly more power at these conditions (450v B+) at only 1.5% THD with 95ma total cathode current (idle), or 22W Pd with a Pd rating of 35W. To get clean power out of EL-34's you have to run them HOT, hence making the E34L from Penta a better choice in the 6CA7/KT77/EL34 family.

Also consider the late Phillips 6BG6:

http://www.vacuumtubes.com/6BG6.html
This completely eliminates the pin 3 problem.  

Jim
WD5JKO

[KC2TAU]

That is interesting. If this is the case then why do folks recommend EL34's as an upgrade to the 6L6's in the Ranger modulator if in such a situation they are being pushed rather hard? The reason I'm leaning towards EL34's is due to the fact that I have them on hand and 6550's cost a fair penny,even the new production items.

[Opcom]

I believe the answer is that the EL34/6CA7 are good when plate currents or voltages are high, up to 150mA or 800V. At 800V in audio service a ceramic socket is important because some of the plastic ones will arc or develop carbon tracks. I've replaced 8417's and 6550's with EL34's in AB1 push pull service and have not blown one yet. In class A service the 6CA7 can't take as much current as the 8417 or 6550 but will do much more than the 6L6. These were Chinese ones from Penta.

If the voltage is not being raised, there does not seem to be an advantage to the 6CA7 in place of the 6L6GC except for the current rating. There is no harm in changing over as long as operating voltages are respected. If the modulated stage is being run at higher current than normal, it might be an advantage.

The 6BG6 with is 900mA heater and 110mA average cathode current rating (85 in typical TV set service -think 24x7) is an inexpensive choice also for low cost and slightly higher current, but at very little real advantage unless increasing the plate voltage. Plate caps always look nice. Someone here may have pointed out the 6BG6 is a 6L6G with a plate cap anyway?

I've used the 6CD6 in several places and it is easy to work with. The later straight-bottle ones are preferred due to higher apparent plate dissipation. The plates are bigger on some anyway. The manual says 20W usually, but they will do a little more. I've used them in 100W audio amps that had 6550's in them and they did OK for voice service. Continuous loud music (sine waves, guitar amps, etc) can overheat the plate a bit. At that point I swapped to EL34's but it was not really necessary. Their advantage is very high current with low screen voltages and low cost.

lots to consider.. but plenty of good choices if there is a reason to change things. You might want to look at the curves and see what the bias (drive volts) and G2 voltage needs to be to obtain the higher current from the tubes under consideration

6L6G/GA/GB heater=900mA, Ik=80mA, G2=270V, plate=360V, dissipation=19W
6L6GC heater=900mA, Ik=80mA, G2=450V, plate=500V, dissipation=30W
EL34/6CA7 heater=1500mA, Ik=150mA, G2=425V, plate=800V, dissipation=25W
6BG6 heater=900mA, Ik=85mA, G2=350V, plate=700V, dissipation=20W
6CD6G/GA heater=2500mA, Ik=200mA, G2=175V, plate=700V, dissipation=20W
6550 heater=1600mA, Ik=175mA, G2=400V, plate=600V, dissipation=35W
7027 heater=900mA, Ik=135mA, G2=500V, plate=600V, dissipation=35W (sell two used ones to a 'phool and buy 4 new 6L6GC's or 8 new EL34's with the $)
6146 heater=1250mA, Ik=150mA, G2=250V, plate=750V, dissipation=20W
8417 heater=1600mA, Ik=200mA, G2=500V, plate=660V, dissipation=35W (sell also to 'phools and buy practical toobs!!)

[KC2TAU]

I really appreciate that information. From what I've read the reason why people run 6550's in Rangers is due to the large power reserves which allows it to provide more modulation. Reading Timtron's article for the Ranger it seems like using the 6CA7/EL34 would allow for an increase in positive modulation.

Here is the quote I'm referencing:

"The stock modulator tubes, 1614 in the first two models and 7027 used in the Ranger II are nothing more than the famous 6L6 but rated for higher voltage. These are tubes with better electrical characteristics than the 6L6 type tubes used. I have used the 6550 with excellent results. These husky tubes can deliver as much as 100 Watts of audio with the plate voltage supply of the Ranger, but the impedance presented to the tubes by the stock modulation transformer will yield enough audio to modulate 120% positive. The large reserve power capabilities of the 6550 will reduce bass distortion caused by the small stock mod transformer.

There are tubes other than the 6550 that can be used with good results such as the 6CA7/EL34 and the 8417. These tubes have a similar pin connection to the 6550 which has the same pin connections as the 6L6."

[WD5JKO]

Good analysis Patrick.

Also remember that the EL34 is a true Pentode. There is a good reason the Pentodes faded away after the introduction of the Beam power tube. Tubes like the 6F6 were replaced with 6V6. At a low B+, a Beam Power tube can swing the plate much lower (below G2) than an otherwise equivalent Pentode. This raises the % efficiency and reduced cost for a given power output. As the B+ rises, this difference diminishes between the two tube families.

Another tube to consider is the 7591/7868/6GM5. These are about the size of a 6V6, have very high Gm, have a 19W Pd rating, and a pair can produce 45 watts audio at 1.5% THD w/o NFB. Today the EH version of the 7591A is available, and a good replacement. You can still fine NOS 6GM5's. These are all called "Power Pentodes", but a close look at them reveals actual beam forming plates for G2.

Jim
WD5JKO

[Opcom]

Jim, Thanks for reminding me about screen current at large plate swings with pentodes vs beam tubes when screen supply voltage is near plate supply voltage. The curves on that Teslovak EL34 bear it out well.

I think the distortion due to low idling current also applies more when the plate voltage is close to the screen voltage and could be helped perhaps by a healthy dose of negative feedback around the circuit from the modulated B+ back to the driver stage provided there is enough gain to overcome it.

I have not had any issues with distortion when running EL34's at cool plate currents and G2=300V/P=650V, but the amps were PA types and used a lot of global negative feedback. The hi-fi amp circuits (Dynaco, Heathkit) did run them very hot with a lot of idling current. Almost class A. I always hated to see a pair of them running red in ultralinear for 35W. what a waste!


It's appropriate to throw this out too for low-power tubes: The below little-used Octal beam tubes are overlooked by the 'phools and everyone else and therefore usually inexpensive. They are not powerful enough for the present application but they individually might be good as audio or video voltage amplifiers, or low level RF buffers or oscillators or just a normal size audio amp.


The 6AU5 and 6AV5 are good beam tubes for low G2 voltages but rated only 10W plate dissipation. They shine well tho' in push-pull right off the 120V line with a bridge or doubler. They are also very short in height which is always convenient.

6AU5 heater=1250mA, Ik=110mA, G2=175V, plate=550V, dissipation=10W
6AV5 heater=1200mA, Ik=110mA, G2=175V, plate=550V, dissipation=11W
They are supposed to be used as horizontal deflection amps but I have never seen a  monitor or TV with one. It would be monochrome no doubt. Not having a plate cap may have something to do with it not being too commonly found in TV sets.

The 6BQ6 is another low dissipation/medium current/high voltage beam tube.
6BQ6/6CU6 heater=1200mA, Ik=110mA, G2=200V, plate=600V, dissipation=11W

Ought to mention the 6W6 and 6K6 as well.
6W6 heater=1200mA, Ik=50mA, G2=165V, plate=330V, dissipation=12W - -Beam Tube
6K6 heater=400mA, Ik=38mA, G2=285V, plate=315V, dissipation=8.5W - -Pentode


I'm intrigued by the smaller Octal power tubes and usually pick them out of 'junk boxes' and get really excited to find a case of them. 3 cases of NOS 12BQ6's were recently had for $50. That is 33 cents each!

[sndtubes]

I don't usually sell my own website or stuff, but I thought I'd make a recommendation as I think it's appropriate.  On my website, I sell some 6BG6GA's that are 1980's production.  I have verified that the internal parts are from the 35 watt 7581A which is a 35 watt version of the 6L6GC.  The main difference is that the plate connection is at the top which will eliminate the problem with high voltage.  I don't think you should have to make any radical changes or biasing changes since these are simply 6L6's with more "headroom". 

I have been selling these for years to guitar players and hi fi guys which either make minor rewiring changes or use an adapter kit I sell.  While I'm not using this in my Ranger right now, I expect they will work quite well.  They're only $10 each or $12 each matched  and they are essentially Philips/ECG (Sylvania) 6L6GC/7581A that have been repackaged as 6BG6GA's.  You can see more at www.vacuumtubes.com/6BG6.html  73, Mike WB0SND

[KC2TAU]

I've looked at that site and they do seem like a very good alternative. I suppose what I'm more looking for is someone who has used EL34's in the modulator section of a Ranger and has noticed improvements over the stock 1614's.

[Steve - K4HX]

Improvements? What sort of improvments? Unless you are going to do the fuill Tron mods and reduce the carrier level of the Ranger, putting in any modulator tube potentially capable of more power is not worth it in my opinion. You will always be limted by the modulation tranformer. And if your input audio is not properly asymmetrical (naturally or processed), the extra audio power does you little good.

[KC2TAU]

Edited.

[KC2TAU]

Something I was thinking about today is that is there any worth in putting a 12BH7 in place of the 12AU7 audio driver in the Ranger?

[The Slab Bacon]

Something I was thinking about today is that is there any worth in putting a 12BH7 in place of the 12AU7 audio driver in the Ranger?

no

[The Slab Bacon]

I got called away earlier and didnt get a chance to post the rest of my thoughts on this.

First of all you have to decide what power level you want to run the ranger at. Keep in mind that a Ranger only has somewhere around 600v of EP to play with.

Next you have to decide how you are gonna use it:
1. an exciter for a leanyour?
2. A low power stand alone rig?
3. A balls to the wall low power stand alone rig?

If you are gonna run it as an exciter or a low power stand alone rig, JUST ABOUT ANYTHING will work acceptably. 6L6s, 1614s, or EL-34s or just about anuthing that will make enough audio to modulate it. The lower the required outpoot, the smaller the modders can be. Short, sweet, and simple!! Remember the KISS rule and make it easy on yourself. Hell, it you are gonna run it as a 10w exciter with the low power mods you might even be able to get away with a pair of 6V6s.

If you are gonna run it "balls to the wall" I would reccomend a pair of 6550s. (even the cheapo chinese ones) They are designed for AB1 service, they dont need any grid current, and all you have to do is tickle the grids with a little audio voltage and away they go! They will work acceptably without any modifications. But if you ditch the driver transformer, convert it to a faze iverter and wrap a little feedback around the modulator they will kick a$$ and take names!! 6L6GCs will also work pretty well at the 600v plate voltage. I have done a few with fuzz inverters and 6550s and they all turned out well.

Do what works for your application, dont try to kill yourself re-inventing the wheel, and dont run yourself ragged trying to get past "the point of diminishing return".

Just my $.02 worth......................................

[KB3DKS]

Hello Mike !
Good talking with you this evening. There got to be too many others on after Chris (JBL) joined in and I just pulled the switch when my ride home got there at 7:30.
  I have been using Sylvania 6CA7 EL34s in the VKII for awhile now and using the LV supply of about 375v for the screens. Those old 6CA7s have a higher scrn rating than most EL34s so it's not a problem. Modulation percentage improved greatly from the stock 807s. You have to watch out with some of the new EL34s as they do not like high scrn voltages. The 2nd gen Tesla E34Ls needed the scrn dropping resistor raised in guitar amps or they would melt down. The original Mullard EL34s could be hard triode strapped scrn to plate with no problem up to at least 475v but don't try that with any of the new Russians or JJs. Speaking of the JJs, their 6L6 is rated for 35 watts plate and I have had very good performance in a couple guitar amps. Not sure what the plate v was but it's higher than any standard old 6L6. You might try a pair of those.
 Hope to catch you on again soon. I usually am listening from 4:00 to 7:30 most nights and the band should be open and clear between us at the earlier time.

73
Bill

[KC2TAU]

I very well may go to 6550's,I just need to pick a pair up. For the foreseeable future I see my Ranger being used as a stand alone transmitter. I have heard about getting rid of the driver transformer and that does seem to be a good idea. I've been working away on the Ranger and clipped some of the capacitors going across the modulation transformer to remove some of the high end roll off.

Now that the modulator resting current has been set properly and that some of these caps have been clipped it certainly sounds better and seems to have stronger modulation. I'm going to be removing all of the roll off caps in time,I'm just going two at a time so that if oscillation sets in I'll have a good idea of what caused it.

DKS - It was great talking to you as well. I understand the concerns regarding the screen voltage on the EL34's and I have been keeping a close eye on the Winged C EL34's that I have been using. I do have a pair of Mullard EL34's but they're reserved for my Traynor YBA-1A once that has been fully debugged. You had a very nice signal on the air and your indoor dipole was working quite well!

I've also noticed that when I make a longer transmission when I speak into the microphone the plate current deflects a little bit higher as time goes on. It only deflects about 5ma more and the power drops by about 5 watts or so so it's quite insignificant. Sounds like a resistor that might be changing value as it heats up?