Are my 6ca7EHs dead?

[johniss0001]

well thing is what i mean tighter power supply 1 would probably increase filtering make the amp sound tighter and well ok you have drake/dagnall transformers in the marshall these transformers really compress under full saturation it's the marshall sound the voltages in a marshall drop as the amp is cranked it's known as the marshall sag. Now on the other end of the scale you have the hiwatts and the laneys also sound citys that use partridge iron those amps don't sag like marshall they sound tighter and to me bigger partridge iron doesn't compress like marshall. sorry demon i got your name wrong in an earlier post i was reading several posts and my vision went a bit funny.

Doug this science project I am not 100% sure this is going to work 100 watt ot you can do on a 50 watt pt and power supply no problem also you have to create the center tap however running 100 watt pt. I am very intrigued by this if it works although logically doesn't look very well.

50 watters and 100 watters are 2 totally diff animals as you know the 50 compresses more and the 100 watter has more headroom but look at the power supply layouts as well.

When i bought my sound city 120 i got it for £30 as the guy toasted the partridge output transformer which is very bloody hard to do as partridges are more robust he did the thing of run the amp on 2 bottles and didn't take impedances into conscideration and that amp has 6 el34s.

Really you should be doing this the other way round you can use a 100 watt pt to run 2 tubes comfortablly with a 50 watt ot however running it the other way around i am not so sure because it's the ot you need to half impedances on. When my sound city 120 blew the output cause of that tosser a tech said to me well you can put a 50 watt ot in if you want to run 2 tubes and a 100 watt if you want to run 4 it's not a problem the pt can handle it...

I am not trying to piss on your parade this is a discussion and most things i've found from experience and if you can get things to work your way and it works and sounds good then i'll take my hat off but as far as a long term thing goes i am not very sure.

[Doug H]

Pulling two tubes never sounded as good as either a stock 50watter or a stock 100watter IMO. Regardless of the impedance matching.

I hope that's not the typical consensus lol, I've never played 100w but I liked the change after playing a 50w for eyars.,

If you were after the C1998 100W sound in a 50W amp, Brian at Marstran is offering 50W clone versions of that transformer for only $99 (or at least, he was) which is the road I would've gone down myself. In fact, I did, but I still haven't fitted it.

I needed a new tranny, George sold these cool replicas, I thought I'd try one on my 50 watter and rematch the output.

I still say, if you're wanting the headroom of a 100W amp, and you're only using two tubes, you need a bigger power supply and different tubes.

Different than the 6ca7s? they are bigger than the el34s I have...ANyhow I'm getting some kt77s for it regardless.

I wasn't after anything other than seeing if it added any vintage 100w mojo to my amp. I know I"m not pushing it and don't have the complexity of 4 tubes, still I thought it sounded cool when I first fired it up. I don't know if it's cause it's big iron or a c1998 spec or whatever. I like the ieda of a big heavy outp0ut tranny. YOu obviously like the OT saturation, I might miss that ultimately, my undrestanding is the 50w can have too much of this. ANyhow, it wasn't a life threatening decision, the tranny could end up in another amp one day etc...I'd miss not being able to hang a 24 ohm resistor on the 32 ohm tap if it was gone, but I might drill a couple more holes in this chassis and try and work something out.

I apreciate all the comments though, sheds some more light on the 50w 100w differenfces. I'm dying to build a 6v6 plexi, or maybe 4 6aq5s.

[demonufo]

The OT doesn't saturate as such in either circumstance. It will create distortion, but not core saturation.

[johniss0001]

not sure how ot's saturate man i think think they have a lot to do with it and a lot more than you think and the steel makes a difference as well e.g. john at sozo made this jtm45 prototype output transformer the maker got the steel wrong and the thing sounded to me really fantastic with plenty of snarle still not right replica iron but it was special.

The thing with the 50 watt is definetly in the pt lower voltages than the supers correct me here didn't early 50 watters have 475+ volts where as the later ones had about 375-400. I have a sound city pa 50 that kicks out around 450 VDC

Doug I recommend if you are doing this as an experiment looking at different transformers like the partridge iron it's very interesting the make up of them and how they compare to the drakes and dagnalls and imo partridge transformers are made better. I love today and how easy it is to get transformers for your amps and kits etc bloody marvelous. To me doug partridge iron doesn't compress as much as dagnall/ drake there is more headroom with them. Look at the old laney supergroup amplifiers they are marshall copies with partridge iron and there is soo much headroom in that amp it sounds huge.

Sorry for hijacking your thread.

Those KT77 I am interested to hear how you get on I am biased to the shuguang/valveart el34b it's my favourite tube in all my vintage amps. So far never had one die, very consistent with no microphonics so far and i've had them in my amps about 2 years. With regards to jjs mate as all tubes just keep an eye on them.

I am very interested in your research and projects please keep me posted

[Doug H]

Sorry for hijacking your thread.

nah, good info

I'm torn between going 400v or 500v+. Mine was a 50w PT of the 475+ variety. I'd olike to try something different. obviously 400v wouold be easier on tubes. there's a martran PT, typical 100w 500v for cheap I've had my eye on, but decisions not made. I'm gonna have to break down and do it soon though, my PT is fried IMO. I've got a lay down lying around but I'm not into drilling a big square hole in my chassis. I'll be checking out those PT.

After this thread I've got half a mind to turn the amp into a quad of 6v6s.

[demonufo]

After this thread I've got half a mind to turn the amp into a quad of 6v6s.

Remember to set the impedance down one step, like you're already doing for the pair of 6CA7's. All you need to alter for the JJ 6V6S's is the bias current.

[johniss0001]

the EH tubes man running 475 on 1 pair is quite a lot of voltage infact i am surprised they have lasted as long as they have sorry i think eh tubes are sub par and well i wouldn't run em on voltages higher than 400v. I had a quad of sovtek el34s in a marshall super pa running 520v at the plates and biased at 34mV per tube sod that they came out straight away! Sovteks are only great for voltages around 400v i would never put them in a vintage amp. JJs not sure i wouldn't touch them again imo i wouldn't use them in amps tbh with voltages over 475VDC

My 50 watt sound city chucks out 450VDC and with el34b biased at 42mV she sings superbly with no signs of stress in the tube the shuguang el34s can take more of a bashing imo and they sound huge i left the bias circuit in that amp stock i can add more resistors to lower it but i am getting good sounds.

If you plan on running 6v6 i'd go with a 375-400VDC transformer to be safe also if you were to switch back to el34 you will have a brown sounding amp with lots of compression due to lower b+

Let's clear something up with power transformers you could use a 500 watt pt if you wanted to do your said power tubes so long as it has a 6.3v winding and the vital windings there wouldn't be a problem to use a single el34 if you wanted it would be the way you wire the output transformer. if you don't "half" the impedances the transformer doesn't see appropriate resistances etc and currents increase and the transformer gets hot. I am very much against this yank 2 tubes and you'll be fine approach i wouldn't want to advise a client to do it they use wrong impedance of cab and they fry their amp it would backlash on to me.

[demonufo]

[quote="johniss0001"
If you plan on running 6v6 i'd go with a 375-400VDC transformer to be safe also if you were to switch back to el34 you will have a brown sounding amp with lots of compression due to lower b+[/quote]
Why bother. The JJ 6V6S (which isn't a true 6V6 remember) can happily handle 500V. I have NO problems running these at 470V all day long.

Also, the Sylvania 6V6's are quite happy to run well over 400V as well (although approaching 450V and over is a BIG ask!). Deluxe Reverbs commonly kick out 440V+, and I don't see these frying tubes all the time, even vintage.

[Doug H]

also if you were to switch back to el34 you will have a brown sounding amp with lots of compression due to lower b+

I can't make up my mind whether I want this or a higher power one. I should be clear, I get 455 on the plates right now with el34s, so I assume the PT is putting out 475+ sans tubes etc... Anyhow, I was thinking of going higher, but that might restrict to JJ 6v6s if I wanted to go that route. hmmm...

[johniss0001]

hmmmm interesting stuff, thanks for clearing me up on those tubes and voltages and a bit about fender amps.

it all depends on what you want to do with the amp doug i've never tried 6v6 tubes i want a marshall to sound like a marshall not an inbetween but as you said this is all an experiment.

[DaveMcLain]

I've tested 6V6's in a 50 watt Marshall and it sounded quite good. I used the EH 6V6's and it just didn't change the tone as much as I would have thought when compared to other things I tested it just didn't have as much headroom.

I've never found B+ voltage to make near as much difference tone wise as it would seem. I have two identical 1974 50 watt Marshalls(numbers are consecutive too) and one has the original mains transformer while the other one has been replaced. The original puts out about 390 volts B+ whereas the one with the new transformer is about 15% higher. In back to back testing I could not find any significant difference in the tone or feel of either amp.

[johniss0001]

dave thats interesting i am not sure how this works for 50's and 100s but i have a 68 laney 100 watter than runs partridge iron ok big difference there and that thing chucks out 600VDC, I have a 70 super pa which is in effect an 8 input superbass that amp has 520VDC now my 78 superbass has around 480VDC and that amp doesnt have as much headroom and both amps i am running exact same tubes and speakers there is a bit more compression. I have a 69 superlead with 475VDC again original iron and that amp compresses like hell and again same tubes and cabs i use.

I found with the higher voltage amps i have there is more headroom and the sound is a tad cleaner granted that maybe due to being shared cathode but with regards to the pa and superbass there is quite a difference my super pa has a bit more clean room and appears to be louder well my super pa has a pre phase master vol (my favourite) and i did a test before i added that to my amp i had my old superbass and set the dials to say vol 2 on identical settings same guitar and cab and the super pa was a lot louder oh both have brand new sets of tubes and they are the same brand

thanks dave that's interesting all round