EL 34's vs. 6550 - Page 2

MartyStrat54 · 02-09-2010, 10:02 PM

Of course, you could do it this way.

American Viking · 02-09-2010, 10:05 PM

Only you would post that here...

Joey Voltage · 02-09-2010, 10:34 PM

Quote:

Originally Posted by MajorNut1967

[COLOR="Lime"]Look everyone who knows, that if you keep a 6550 on a shorter leash that it is less likely to fail hence the the (150k). But the same goes for a lot tubes including the KT88 would benefit. But the point being of the 20 or so JCM 800's I have worked on personally I have never seen the 150k split on any of them and you show me an Official Marshall Service book or Manual that show them? Now go do the Cha Cha with my Sister, you empty headed animal.

Oh, I have seen this. in real models, and if you look on page 207 of the history of marshall book, you will see an official schematic showing this. It's not that you are keeping the 6550 on a shorter leash, it's that you are using only slightly below the maximum limiting values as quoted on the Data sheet from the manufacturer of the valve, they don't put that shit there just so you ignore it.

, for example try running the screens of an EL-34 at 600VDC, and see how long it lasts you, not very I imagine, and it's not because you are keeping them on a shorter leash by running them at or below the recommended 450V, rather than you are operating them outside their maximum ratings at 600V.

Note that 150K grid load for fixed bias operation of a 6550 is only applicable towards the 6550C (the most common modern type) which quote a maximum of 200K, other versions of the 6550 such as the 6550A will often quote as low as 50K maximum grid load for fixed bias operation.

Quote:

Originally Posted by MajorNut1967

Point Two: I am with Marty, "why didn't Marshall use the US 6CA7 as it is much closer to the EL34!" We may never know, maybe New York had a tube deal with GE.

Mary answered his own question, because of economics. they already were importing 6550's, or it was a common tube being made domestically in europe (Siemens), so importing yet another tube from the US, just to end up shipping it back enevitably would have been more expensive to do, and it was just supposed to be a quick fix. It's the same reason you see 25KL presence pots in later models instead of 5KL. It is already on the BOM for a mid pot! why inflate the BOM?, and whereas the only trade off versus economic gain for using a 25KL presence pot is that you just have to turn it up more before it has a noticeable effect (25KL actually isolates the presence cap too much from ground, so it's not effective until the last half of sweep), there would be a HUGE trade off for using 5KL for a mid pot..... It would change everything.

Joey Voltage · 02-09-2010, 10:35 PM

Quote:

Originally Posted by MartyStrat54

Of course, you could do it this way.

yeah but that is WAAAYYYYYY messier

dread1 · 02-09-2010, 11:03 PM

That is SICK......

solarburnDSL50 · 02-09-2010, 11:26 PM

Quote:

Originally Posted by Joey Voltage

Oh, I have seen this. in real models, and if you look on page 207 of the history of marshall book, you will see an official schematic showing this. It's not that you are keeping the 6550 on a shorter leash, it's that you are using only slightly below the maximum limiting values as quoted on the Data sheet from the manufacturer of the valve, they don't put that shit there just so you ignore it.

, for example try running the screens of an EL-34 at 600VDC, and see how long it lasts you, not very I imagine, and it's not because you are keeping them on a shorter leash by running them at or below the recommended 450V, rather than you are operating them outside their maximum ratings at 600V.

Note that 150K grid load for fixed bias operation of a 6550 is only applicable towards the 6550C (the most common modern type) which quote a maximum of 200K, other versions of the 6550 such as the 6550A will often quote as low as 50K maximum grid load for fixed bias operation.

Mary answered his own question, because of economics. they already were importing 6550's, or it was a common tube being made domestically in europe (Siemens), so importing yet another tube from the US, just to end up shipping it back enevitably would have been more expensive to do, and it was just supposed to be a quick fix. It's the same reason you see 25KL presence pots in later models instead of 5KL. It is already on the BOM for a mid pot! why inflate the BOM?, and whereas the only trade off versus economic gain for using a 25KL presence pot is that you just have to turn it up more before it has a noticeable effect (25KL actually isolates the presence cap too much from ground, so it's not effective until the last half of sweep), there would be a HUGE trade off for using 5KL for a mid pot..... It would change everything.

Joey called Marty a "Mary"...

MartyStrat54 · 02-09-2010, 11:47 PM

I'm man enough to handle it. It won't be the first time.

Gibson+Marshall=Heaven · 02-10-2010, 06:36 AM

So allow me to take this question back to basics for sec. I am currently having my 4104 EL-34's changed over to 6550's. The tech I'm using will bias it properly, but should I let him know about this resistor information? It sounds like depending on which one is in my amp, the 6550's might not last very long? Is that accurate?

shampoch · 02-10-2010, 07:28 AM

What an awesome response to this thread - here are some more board pics. I have been informed by the previous owner of my amp through email (who had it store for 15 years) he thinks he had the amp switched over to EL34's. He bought it used so who knows what was in it from the factory. The tech he used is supposedly very reputable and has been recognized nationally. I have a bias rite on the way so I can re-tube and see what I have. All the help is appreciated!

American Viking · 02-10-2010, 08:44 AM

Quote:

Originally Posted by Gibson+Marshall=Heaven

So allow me to take this question back to basics for sec. I am currently having my 4104 EL-34's changed over to 6550's. The tech I'm using will bias it properly, but should I let him know about this resistor information? It sounds like depending on which one is in my amp, the 6550's might not last very long? Is that accurate?

It couldn't hurt. After everything we've gone over I would. Just make sure the grid resistors are 220k for the EL34's and if the range resistor needs to be changed your tech will make that call when he's biasing it.

Joey Voltage · 02-10-2010, 10:34 AM

Quote:

Originally Posted by shampoch

What an awesome response to this thread - here are some more board pics. I have been informed by the previous owner of my amp through email (who had it store for 15 years) he thinks he had the amp switched over to EL34's. He bought it used so who knows what was in it from the factory. The tech he used is supposedly very reputable and has been recognized nationally. I have a bias rite on the way so I can re-tube and see what I have. All the help is appreciated!

if it was an 86, EL-34's. I had an 86 for many years before it was stolen. I bought mine used too, but it still had the original quartet of EL-34's it was shipped with 12 years prior.

The one thing with later models though.... particularly the 100W, is that Marshall switched the powersupply around a little, and as a result the preamp supply voltages are pretty high, about 80v higher than some of the earlier ones which make them cleaner and brighter sounding.

dread1 · 02-10-2010, 12:12 PM

Here's a pic of mine. I think I'll leave this bias swap up to a tech.I have a shoebox of the good resistors (pihers) but not sure really which one to put in the place of the existing resistor. Plus, there's no room for those big hogs in the headbox

I don't want the next post to be, "big spark and burning smell" or even worse 1981 2204 dead, will sell cheap. I have no problem saying I'm clueless and need to learn more before I blow my amp.

dread1 · 02-10-2010, 12:14 PM

Of course if someone knows what would go there, I could look in the box of resistors I have and bring them to the tech. I have no problem using the multi meter and getting numbers.

Joey Voltage · 02-10-2010, 02:21 PM

Quote:

Originally Posted by dread1

Here's a pic of mine. I think I'll leave this bias swap up to a tech.I have a shoebox of the good resistors (pihers) but not sure really which one to put in the place of the existing resistor. Plus, there's no room for those big hogs in the headbox

I don't want the next post to be, "big spark and burning smell" or even worse 1981 2204 dead, will sell cheap. I have no problem saying I'm clueless and need to learn more before I blow my amp.

looks like it was shipped with 6550's as you see the reputed 150K loads, but it does no harm to keep those in for EL-34's... might actually be better since EL-34's are a very sensitive tube any way so it takes less to drive them to full output.

MajorNut1967 · 02-10-2010, 02:25 PM

Quote:

Originally Posted by Joey Voltage

Mary answered his own question, because of economics. they already were importing 6550's, or it was a common tube being made domestically in europe (Siemens), so importing yet another tube from the US, just to end up shipping it back enevitably would have been more expensive to do, and it was just supposed to be a quick fix. It's the same reason you see 25KL presence pots in later models instead of 5KL. It is already on the BOM for a mid pot! why inflate the BOM?, and whereas the only trade off versus economic gain for using a 25KL presence pot is that you just have to turn it up more before it has a noticeable effect (25KL actually isolates the presence cap too much from ground, so it's not effective until the last half of sweep), there would be a HUGE trade off for using 5KL for a mid pot..... It would change everything.

Um Marshall wasn't Importing the tube to the UK, the Amps were sent to New York without Power Tubes and the were installed at Korg/Univox. The reason that they stopped shipping amps with EL34's was because the were having EL34 arriving broken or lasting a week and dying. I make no sense at all for Marshall to Import tube from the US (6550 is a US tube) and then take the chance of having the 6550's broken in shipping. The issue was tube failure not economics. I know they did this for sure a friend of mine worked at Korg/Univox in the early 80's and for a while that was his job for a year & a half!

As far as the Pres Pot you would know more then me. But wasn't the Marshall MID Pot always 22K in the old days?

dread1 · 02-10-2010, 02:26 PM

I actually bought a set of el34's yesterday and it only biased up to 15.0ma max.

MajorNut1967 · 02-10-2010, 02:38 PM

Quote:

Originally Posted by MartyStrat54

"Hello there Major."

Cheers Mate, what you BLoody miss me? NOT! lol Hope all is well for you Bro!

Major PAIN

MajorNut1967 · 02-10-2010, 02:40 PM

Quote:

Originally Posted by solarburnDSL50

Joey called Marty a "Mary"...

OHH I just noticed that I'm not in trouble this year yet, so I'll bloody behave!

Mr. BA

Joey Voltage · 02-10-2010, 04:13 PM

Quote:

Originally Posted by MajorNut1967

[COLOR="Lime"]Um Marshall wasn't Importing the tube to the UK, the Amps were sent to New York without Power Tubes and the were installed at Korg/Univox. The reason that they stopped shipping amps with EL34's was because the were having EL34 arriving broken or lasting a week and dying. I make no sense at all for Marshall to Import tube from the US (6550 is a US tube) and then take the chance of having the 6550's broken in shipping. The issue was tube failure not economics. I know they did this for sure a friend of mine worked at Korg/Univox in the early 80's and for a while that was his job for a year & a half!

Well if that's the case then..........

Still might have been economics, as they were already using 6550's in some models although I did a little research and found that the USA (notably GE) ceased production of the 6CA7 in the 70's sometime, Sylvania might have too. And it was my understanding Marshall did this in the 80's as a quick fix. regardless, the 6CA7, while has similar ratings and characteristics as an EL-34, it is still a different sounding tube.

Quote:

Originally Posted by MajorNut1967

[COLOR="Lime"]As far as the Pres Pot you would know more then me. But wasn't the Marshall MID Pot always 22K in the old days?

yeah thats the point I was making. it was the presence pot, which was traditionally 5K, that was changed to the 22K/25K value. If you already have the 22KL on the BOM for the mid pot, and the only down fall for using that same value for the presence pot too is that it just starts working a little later, but the end result is the same, then why inflate the BOM with another component.

conversely, If you happened to use a 5KL pot for a mid pot, it would be completely useless.

ironlung40 · 02-10-2010, 09:12 PM

Quote:

Originally Posted by Wilder Amplification

The funny thing about this is that SOME USA Marshalls that had 6550s installed by the distributor actually had 150K resistors that look like they came from Marshall that way. Either they came from Marshall like that (some official Marshall schematics reflect that), Unicord was smart enough to install the same exact resistor type of that value, or some really smart tech that happened to have that same resistor type of the 150K value knew to install those with 6550s.

What else do you know good/bad about unicord distributed Marshalls? I've got a 1981 year Unicord 2203.

Joey Voltage · 02-10-2010, 10:02 PM

Quote:

Originally Posted by ironlung40

What else do you know good/bad about unicord distributed Marshalls? I've got a 1981 year Unicord 2203.

there is nothing bad, they were just the NA distributor trying to protect their investment. All possible circuit changes to the best of my knowledge were all done at the marshall factory before export, with the exception of fitting the tubes as pointed out by major. I highly doubt Unicord had anything to do with circuit modifications once they had them. on some of those Marshalls you will even see a USA export stamp.

Note again, and I will keep on drilling this, 150K for a 6550 is meaningless and potentially just as harmful if that vlaue exceeds the maximum limiting value for the 6550 used. although The 150K value is perfectly acceptable for an EL-34, and may even be encouraged for a number of reasons.

MajorNut1967 · 02-11-2010, 09:13 PM

Again I said something absolutely ridiculous and no one called me on it! LOL
"Korg/Univox" UNIVOX! Heeee Heeee.

MartyStrat54 · 02-11-2010, 09:47 PM

Quote:

Originally Posted by MajorNut1967

Again I said something absolutely ridiculous and no one called me on it! LOL
"Korg/Univox" UNIVOX! Heeee Heeee.

I just got back over here you old sea wart. UNIVOX...don't they make banjo's?

solarburnDSL50 · 02-11-2010, 09:49 PM

This happened to be over at the "other amps" forum here.

MartyStrat54 · 02-11-2010, 10:04 PM

Good grief! That guitar amp had seven tubes and they were all preamp tubes. It's a hybrid with SS power section. I read where they made a "B" Series and they were all tube. Of course, if you look at the company history, they basically were pirates. They stole designs and copied every guitar known to man. I had one of their Les Paul copies and it wasn't bad. It had a mahogany and maple body and was as heavy as a regular LP.

Look here at these amps. Some had nine tubes and a "SS" power section. Go down a little and the "B" amps were made like 1971. Hell, I was a junior in high school then.

Univox Amplifiers

MajorNut1967 · 02-11-2010, 10:10 PM

Quote:

Originally Posted by MartyStrat54

I just got back over here you old sea wart. UNIVOX...don't they make banjo's?

weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee hhhhhhhhhhhhhhhhhhhhhhaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaawwwwwwwwwwwwwww

ironlung40 · 02-11-2010, 11:12 PM

I don't know where all of you boys are from, but down here in TN this is what piggybacking is!

http://img51.imageshack.us/img51/1737/pigrider.gif

MajorNut1967 · 02-12-2010, 12:28 AM

Quote:

Originally Posted by ironlung40

I don't know where all of you boys are from, but down here in TN this is what piggybacking is!

http://img51.imageshack.us/img51/1737/pigrider.gif

LOL If that hog was around my people we'd a had that sum bitch wrapped in banana leave and roasting in the ground.

CKCinMass · 02-12-2010, 05:12 AM

Quote:

Originally Posted by dread1

Can someone post a pic of a piggyback application of the bias resistor?

Here is a shot of a piggy back job. Unfortunately the "tech" I used, installed a piggy back when there was absolutely no need to piggy back resistors since there was no change in output valve types. This amp went in with EL34's and came back with EL34's. The "tech" had biased my valves extremely hot (how they lasted as long as they did is beyond me). Once I removed the piggy back resistor, I was able to properly bias.

American Viking · 02-12-2010, 03:39 PM

Quote:

Originally Posted by CKCinMass

Here is a shot of a piggy back job. Unfortunately the "tech" I used, installed a piggy back when there was absolutely no need to piggy back resistors since there was no change in output valve types. This amp went in with EL34's and came back with EL34's. The "tech" had biased my valves extremely hot (how they lasted as long as they did is beyond me). Once I removed the piggy back resistor, I was able to properly bias.

I can't speak for your tech but I can say this... All tubes aren't created equal even if they are of the same type. If one set of tubes is too "cold" then you may have to piggyback to be able to get them within the proper range. All that resistor does is control the amount of current that can go to the tubes. It is not the be-all-end-all of tube swapping by any means. Typically though, you are right, there is no need to change it but it some cases it's a possibility.

My only question is, if you know how to bias, then why did you have someone else bias it for you? It seems odd that anyone would mess up the formula so bad they would run 'em too hot. Tubes are all matched quad or pair, right?

02-09-2010, 10:05 PM	#32 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,038	Re: EL 34's vs. 6550 Only you would post that here... __________________ ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

02-09-2010, 11:03 PM	#35 (permalink)
dread1 Senior Member Join Date: Sep 2008 Posts: 418	Re: EL 34's vs. 6550 That is SICK......

02-10-2010, 06:36 AM	#38 (permalink)
Gibson+Marshall=Heaven Junior Member Join Date: Jan 2010 Posts: 12	Re: EL 34's vs. 6550 So allow me to take this question back to basics for sec. I am currently having my 4104 EL-34's changed over to 6550's. The tech I'm using will bias it properly, but should I let him know about this resistor information? It sounds like depending on which one is in my amp, the 6550's might not last very long? Is that accurate?

02-10-2010, 07:28 AM	#39 (permalink)
shampoch Junior Member Join Date: Dec 2009 Posts: 9	Re: EL 34's vs. 6550 What an awesome response to this thread - here are some more board pics. I have been informed by the previous owner of my amp through email (who had it store for 15 years) he thinks he had the amp switched over to EL34's. He bought it used so who knows what was in it from the factory. The tech he used is supposedly very reputable and has been recognized nationally. I have a bias rite on the way so I can re-tube and see what I have. All the help is appreciated! __________________ 65AMPS SoHo \| Bogner XTC Classic \| Diezel VH4 \| Soldano SLO \| Vibro~King \| VHT Pittbull UL \| 5150 II \| 1986 Marshall JCM800 2205\| 1983 Marshall JCM800 2204 \| Zwengel Banshee 50 \| 2010 Mesa Dual Recto

02-10-2010, 12:14 PM	#43 (permalink)
dread1 Senior Member Join Date: Sep 2008 Posts: 418	Re: EL 34's vs. 6550 Of course if someone knows what would go there, I could look in the box of resistors I have and bring them to the tech. I have no problem using the multi meter and getting numbers.

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02-10-2010, 02:26 PM	#46 (permalink)
dread1 Senior Member Join Date: Sep 2008 Posts: 418	Re: EL 34's vs. 6550 I actually bought a set of el34's yesterday and it only biased up to 15.0ma max.

02-11-2010, 09:13 PM	#52 (permalink)
MajorNut1967 Senior Member Join Date: Jul 2009 Location: South Pacific Posts: 1,661	Re: EL 34's vs. 6550 Again I said something absolutely ridiculous and no one called me on it! LOL "Korg/Univox" UNIVOX! Heeee Heeee. __________________ MJN1967 aka BA (Bad Attitude) 1958 Fender 5E3 Deluxe 1968 model 1987 50watt. A Baby Major (Half-Power) I built from the ground up. JTM 45 Clone combo Ground up build. JCM 800 Clone Ground up build, with Wilder Mods. Custom Built Warmoth Strat 75' Fender Tele-Deluxe '70 style strat custom build w/Custom Shop 69's PU's

02-11-2010, 11:12 PM	#57 (permalink)
ironlung40 Senior Member Join Date: Nov 2008 Location: TN Posts: 953	Re: EL 34's vs. 6550 I don't know where all of you boys are from, but down here in TN this is what piggybacking is! http://img51.imageshack.us/img51/1737/pigrider.gif

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