Author Topic: how to tell if valves need replacing? (Read 7916 times)

gwEm · « **Reply #15 on:** December 16, 2005, 01:25:39 PM »

ok, so i have changed the tubes and its much nicer now ;) maybe i should have done it straightaway, but not being experienced in how valves 'should' sound, i thought it best to ask. anyway, i learnt some things from the discussion so no regrets.

t3haze: it has a valve power amp and output transformer, read up the thread for full details ;)

heavier than hell: thanks for this tip, maybe i can use it in the future.

tweboss: actually i have replaced the 12ax7 with a 12at7 and its still gainy as hell ;) the solid state input stage already has a pretty high gain in the cream machine. even now its impossible to get a totally clean sound without rolling down the volume on my guitar slightly. maximum gain setting drives the preamp into over the top spitting and fuzzy saturation.

i understand op-amps pretty well at least, so time to whip out the soldering iron...

PhilKing · « **Reply #16 on:** December 16, 2005, 01:36:11 PM »

There is the 12AY7 - this gives about 45% of the gain of the 12AX7. Don't know if it would help though if the sound is already boosted before it gets here. There is also a possibility that you could try this pr a 12AV7 as the power tube to give you more headroom. But I am not sure of the build of the Cream Machine, so I would see if there is a forum somewhere that might help you.

gwEm · « **Reply #17 on:** December 16, 2005, 01:45:24 PM »

you read my exact thoughts philking :)

actually i get the feeling from playing the amp that the 12AU7 tube is working really well in the power amp.

i tried the old 12AU7 in the preamp, and it was not enough gain (would be good for blues though i reckon). which suggests the 12AY7 to me also. its good to know i'm thinking on the right lines.

anyway, i found the schematics for the box, so it shouldn't be too hard to make adjustments. i have the hunch the solid state gain stage is pushing the first half of the preamp valve into saturation. the gain control is between both halves of the 12A?7 preamp, which backs up this impression.

tewboss · « **Reply #18 on:** December 16, 2005, 05:07:54 PM »

The EH English Muff'n has one 12AX7 and one 12AY7, and is supposed to be really nice.

Floyd Pepper · « **Reply #19 on:** December 17, 2005, 01:11:46 PM »

Quote

There is the 12AY7 - this gives about 45% of the gain of the 12AX7

PhilKing, Can any amp that takes 12AX7s take 12AY7s? Can I put 12AY7s in my Marshall for example?

PhilKing · « **Reply #20 on:** December 18, 2005, 01:23:19 PM »

Usually you can swap the 12A-7 series, the 12 gives you the heater voltage. Going with a lower gain should not be a problem, but HJM is more up on the specifics of this than I am.

gwEm · « **Reply #21 on:** December 18, 2005, 04:35:34 PM »

was playing the cream machine with the new 12at7/12au7 all morning. on consideration its pretty sweet like this, and i think i might leave these valves in for a while, as i can get a number of cool tones. i especially think the 12au7 power amp is great :)

it does need a gentle touch to get a clean tone, but thats nice somehow.

really enjoying my little rig:

Floyd Pepper · « **Reply #22 on:** December 18, 2005, 08:47:31 PM »

Nice wall paper. :)

gwEm · « **Reply #23 on:** December 19, 2005, 01:46:35 PM »

yeah, its listed in the inventory too ;) no chance to change it :(