Distorted MC275 vi

[sandbites]

Sound coming out off my mc275vi is a little grainy... sounds like there’s 10% sand in the music. It’s also about 10% distorted. It doesn’t happen right away it’s a little fine when starting from cold. Then it gets worse when it warms up after 18 minutes

Can I solve this be changing the tubes. Do I change just the KT88s even the small tubes?

[NZ421291]

Its almost always the Tubes- & usually the biggies.

Check them first.

[FreddieFerric]

Originally Posted by sandbites

Sound coming out off my mc275vi is a little grainy... sounds like there’s 10% sand in the music. It’s also about 10% distorted. It doesn’t happen right away it’s a little fine when starting from cold. Then it gets worse when it warms up after 18 minutes

Can I solve this be changing the tubes. Do I change just the KT88s even the small tubes?

The signal tubes can be tested on a good tube tester. As I understand it a tube tester cannot put enough plate voltage on the power tubes to tell which one is bad.

Two options here. Replace them all at one time or take the time to roll out one at a time to until you find the culprit. The problem with option 2 is that you start to have tubes with differing hours on them. I would opt for option 1 personally.

[Msegal]

Originally Posted by FreddieFerric

The signal tubes can be tested on a good tube tester. As I understand it a tube tester cannot put enough plate voltage on the power tubes to tell which one is bad.



Two options here. Replace them all at one time or take the time to roll out one at a time to until you find the culprit. The problem with option 2 is that you start to have tubes with differing hours on them. I would opt for option 1 personally.

+1

[tdelahanty]

Originally Posted by FreddieFerric

The signal tubes can be tested on a good tube tester. As I understand it a tube tester cannot put enough plate voltage on the power tubes to tell which one is bad.

Two options here. Replace them all at one time or take the time to roll out one at a time to until you find the culprit. The problem with option 2 is that you start to have tubes with differing hours on them. I would opt for option 1 personally.

If you have access to the proper tube tester it will test output tubes at the correct plate voltage. Especially an industrial/professional Hickock tester from the golden age of tubes.

[miner]

Option 1 above or you will be chasing tubes approaching their death cycle for years

[FreddieFerric]

Originally Posted by tdelahanty

If you have access to the proper tube tester it will test output tubes at the correct plate voltage. Especially an industrial/professional Hickock tester from the golden age of tubes.

Sorry, that's a no go. It won't tell him what he needs to know. My friend Richard Gray is one of the most experienced tube men around today. My statement made in my post is based on words directly out of his mouth when I was having the same issue with 6550's.

If the OP wants to chase this dragon I'd suggest he start here:

http://www.tronola.com/html/testing_..._lab_eqmt.html

[tdelahanty]

Originally Posted by FreddieFerric

Sorry, that's a no go. It won't tell him what he needs to know. My friend Richard Gray is one of the most experienced tube men around today. My statement made in my post is based on words directly out of his mouth when I was having the same issue with 6550's.

If the OP wants to chase this dragon I'd suggest he start here:

http://www.tronola.com/html/testing_..._lab_eqmt.html

I found your remarks quite interesting. A friend used to bring me his AR D150 once or twice a year to check and re-bias its tubes. I finally decided not to do this any longer due to the risk of very high voltages and weight. I was educated and worked professionally in the field of electronics for 33yrs. The last thing I would recommend to a hobbyist is a patch-work bread board with lethal voltages. I care not for Richard Gray's opinion!!!

[FreddieFerric]

Originally Posted by tdelahanty

I found your remarks quite interesting. A friend used to bring me his AR D150 once or twice a year to check and re-bias its tubes. I finally decided not to do this any longer due to the risk of very high voltages and weight. I was educated and worked professionally in the field of electronics for 33yrs. The last thing I would recommend to a hobbyist is a patch-work bread board with lethal voltages. I care not for Richard Gray's opinion!!!

I don't come to these forums to argue with other members, but I do try to help others whenever I can. You go on and believe anything you wish to. I'll do the same and we'll leave it at that.

[W9TR]

I’ve got three MC 2301’s and an MC 275V. Count ‘em if you care to but that’s a lot of tubes! So I’ve been to this movie a bunch of times.

My advice - get a complete set of tubes and replace the entire amp set all at once. If the issue persists then you are looking at a service call. If not, you are golden and can enjoy your amp for many moons.

If you don’t already have one, buy an hour meter so you know how many hours are on your tubes. It’s just a nice thing to know, not critical.

The plate voltage on my MC 275V measures 470Vdc @ 120Vac line. The MC 275vi is even higher at 500Vdc. Great care must be exercised....