Hi all, new to the forum.

I bought a 1987 off a my local forum (AGGH), it's been passed around a few members, so I'm not sure of any mods and such, but I have a few questions all the same.

The day after I got it it blew a HT fuse, I emailed Nik for the correct rating/type, and got a new one. I'm not sure if this has happened before or since, but one power valve looks blown i.e bottle is white in colour and doesn't glow. The amp still works, but would it cause damage to the amp running it on only one power valve?

Also I'm interested in what bran of valves people recommend.

Cheers,
Al.

What Wyatt said!

You must NOT operate it with 1 tube

The white powder thing indicates it's gone, most likely thru breakage (shipment?)

You need to replace (get a matched pair, good ones are at most USD 30 a pair, JJ etc), and rebias the amp with the new tubes.


Thanks!

nik

Hi

Tubes are wearables, same  way your strings are.

You do need to change them from time to time.

And, when you change, some amps do need to be rebiased for the new tubes.

As for the 18W, thats cathode biased amp, just get a matched pair of EL84s.

But all in all, you do have to change the tubes, they wont last forever.

We get the JJs from Eurotubes, and they're pretty much one of the best dealers for JJ, if not the best. Ie, they do test, and match, which is important.

It is important to get tubes from good source. I do hear stories when ppl buy matched tubes from ebay or other online stores, only to discover they're off by 15mA for the bias.

pricier by USD 2-3, but would be better, in the long (even immediate) run.

Thanks!

nik

I agree with the earlier post in that you need to buy a couple of pairs and try them to see what it sounds like and what you find that you like best.  The nice thing about the 50 watt head is that you only need two output tubes so it's less expensive to try different things.  Put them in there and bias the amp.

I've experimented with a lot of different output tubes in a 50 watt Marshall and I tend to like the JJ E34L's about the best if you're going to use an EL34.  I tend to like the EH tubes but I don't like their EL34 very much yet their 6CA7 is quite good sounding. 

Hi Thats cool Al

But biasing cold wont hurt the amp or cause it to blow a tube.

I suspect the tube got hit in shipment, and broke.

Thats what the white powder stuff is.

Anyways do keep us posted on how it goes?

Thanks!

Nik

I don't think the amp tech was talking about it being biased cold he was talking about it being biased very hot.  Instead of -35 or so volts on the grid he was only seeing -20's and thus unable to properly bias the tube and reduce it's idle current to an acceptable level. 

Just my thoughts. 

In today's world I've found it to be quite common to have to change a resistor or two in the circuit to allow the bias pot to "scale" correctly for the tube of choice.

go online to one of the upper mentioned tube stores or just good 'ol ebay.

buy your self a set of ELECTRO HARMONIX [EH] 6CE7 tubes and EH 12AX7'S and dont look back.

i have used them all, love many, wouldnt use some for paper weights [jj's come to mind, especially their pre amp tubes] but i can say without batting an eye that when i put my first set of the EH 6CE7/12ax7 in my ceriatone 1987, COMPLETE difference! all those little under tones that i heard from my heroes marshall amps just wasnt there before, no matter what i tried.

then, i put in that set and WHAMO!! there it was. about two weeeks later i find out edward vanhalen had the same issue. he heard that pete townsend used them exclusively in his amps and that is where ed's brown sound made its final touch, the 6CE7's that he didnt reveal until not long ago.

i had winged C EL34's and tung sol 12ax7 in it. GREAT combo also. but the EH combo of 6CE7 and 12ax7 just put the amp over the top and i get EVERY marshall tone from my heroes [the british ones anyways] now.

just do it. then i will send you my info so you can add me to your will.