need some knowledge.....

[z28lt16]

I'm new here and just purchased a MarkIV used from a buddy of mine who was not using it.

I really like the amp so far. Ive had it a couple weeks now, and i'm just getting acquainted with it.

I am new to tube amps and the question I have right now. Is yesterday while I was playing it I decided to look behind it and look at the tubes. Now I can see the front ones but the back ones are kinda tough too see. While looking at the front ones the far left one was not really bright like the other 3. And as i said I tried looking behind at the back ones but it was hard to tell if those were all lite. Would this indicate a bad tube.

Now I have not cranked this baby yet. Thats what I really need to do. Now would this make a difference as far as tube brightness.

This amp is a A version from the early nineties. Basically I really hope to gain knowledge here.

thanks for any help---dy

 

[visualrocker69]

You came to the right place!
...but I'm new to tube amps too I also have a Mark IV, but I'm in the process of switching from widebody combo to short head.

By the way, the big tubes in the front in are the power tubes and the little ones are preamp tubes.

 

[z28lt16]

Mine is a short head I believe. It was converted from a combo. He even gave me the old case that he originally had with the combo.

So yes visual it must be a power amp tube then. How can you see the pre amp tubes. By looking back there its kinda tough.

Good luck with your switch

 

[visualrocker69]

Dunno - haven't gotten to switching tubes yet. Though I already did loads of research and I know EXACTLY what tubes I'll be swapping mine with when the time comes. So I guess I need to find out the practical aspects of how to swap and get back there by then... :?

 

[Whoopysnorp]

In my experience preamp tubes can sometimes vary in brightness. The question is, are they all equally hot to the touch?

 

[z28lt16]

this would be a power amp tube I believe. 1st one on the left. It hardly had any brightness to it at all. Maybe it needs to get cranked for it to glow.

Experimenting with this amp is going be fun.

 

[Boogiebabies]

I don't think cranking it would be a good idea yet. When in doubt, change it out. It could be a duller than normal heater filament, or the rare occasion, a failing heater filament. Sometimes, the heater is not fully visable from the top of the tube, probably like what you are seeing. If it does not fully extend out it will not appear to glow orange at the top like the others. I would let the amp heat up for 5 minutes in standby and then flip on the mains and cut the lights.
If the inner two are glowing a nice even blue and the outer two a similar, but maybe more intense blue, the tubes are probably operating normally. If one does not have a blue glow, it's near the end of its life. Cranking the amp may bring impending doom as it can shake the heater wire to short into the plates and it's lightning in a bottle and the gray plates will glow cherry red until your fuse blows.
It's a 50/50 chance with old tubes. Preamp tubes can all glow at different levels. Some flash at startup and some barely show a glow.
They can either work for years, blow up, make weird noises or pass no signal at all.
Welcome to the world of thermionic valves.

 

[z28lt16]

Thanks Boogiebabies for the info.

Normally I have been letting it warmup a minute or 2 then I 've been putting on the mains. I'll let it sit in standby for 5 and then check the color of the front tubes..

hopefully they will be glowing nice and blue.


thanks dy

 

[ToneAddictJon]

I'm not sure if my Mark IV is just odd or not, but the front grill is removable to get to the preamp tubes (held on by velcro and came with a black grill and wheat grill), I just push in on the top or bottom of the front grill until I can get my finger under it to pull it off. My footswitch is also held on by velcro on the back, but then again I did buy it from a guy that custom ordered it from boogie back in 93-94 so who knows

 

[Boogiebabies]

That's from the factory. It's absolutly genius.
There is no bigger pain in the *** than to have to change pre's in a short head. I flip mine upside down and pull the power tubes and it is still worse than putting a starter in an 88 Saab 900.

 

[ToneAddictJon]

So is that normal or a custom option BB??

 

[z28lt16]

Tone I dont think mine has that. Either that or i'm just pulling on the grille mesh part wrong. Seems like its on there pretty tight. And to get to my footswitch stuff it looks like a few phillips screws. No velcro there either.

They must have had different color options because my boogie letters on the amp are grey and it seems like I have mostly seen white letters on other amps

 

[z28lt16]

hey boogiebabies that starter in that saab cant be as bad as pullin plugs in a LT1.

 

[disassembled]

hey boogiebabies that starter in that saab cant be as bad as pullin plugs in a LT1.

I know for a fact it can't be as bad on an LS1 with a CAS TT kit installed. (starter or plugs).

Greg

 

[z28lt16]

oh TT's on a gen4 nice. Not easy but worth it when its done. I guess most of the TT's have to be removed for access.

 

[z28lt16]

well I took boogiebabies advice and let the amp stay on standby for 5 mins. Well absolutely no glow what so ever on that one. I believe it is not even funtional. I played the amp for about 15 mins and the tube was cold to the touch.

looks like new tubes for me