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my new old tube amp--help!

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(@wes-inman)
Illustrious Member
Joined: 18 years ago
Posts: 5599
 

Well, it certainly can't hurt to replace the tubes, those may be very old and on their way out. You will almost certainly notice the amp is much louder with new tubes.

It could be another problem. The volume on my Marshall amp would fade out. The preamp tubes were very dim as well. It turned out I had to have the bridge rectifier replaced. Cost quite a bit, but the amp sounds fantastic now.

As far as breaking up (good Blues tone), you may be able to substitute tubes that breakup earlier. I am kinda surprised the amp does not overdrive at all. But tube saturation is not to be compared with modern distortions.

Here is a clip of the Epiphone Valve Junior combo. But it is a good example of tube amp overdrive.

http://www.youtube.com/watch?v=hAP3AD6TwcE

It might be worth taking the amp down and letting a tech go over it.

If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis


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 Anonymous
Joined: 52 years ago
Posts: 0
Topic starter  

Thanks for your reply Wes.

This is my first tube amp but I can nonetheless tell a tube amp when I hear one (huge vintage blues/rock fan here). There really is no overdrive... The sound doesn't fade out either so I don't think I have the same problem as you did.

I'm going to replace the tubes and then if the situation doesn't improve I'll go see an amp tech.

It sucks because I paid quite a bit of money for an amp that old thinking that it would be fully functional... I guess I should have asked more questions to the seller before bidding on it :(


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(@lunchmeat)
Estimable Member
Joined: 16 years ago
Posts: 153
 

Little breakup and bassy response?

Perhaps it's a speaker problem? You might have high-output speakers that your amp can't overdrive. Usually, the wattage of an amp is rated to twice the speaker's max load; check and see if they are (this is if you're using a head and an external speaker).

Just my guess, I'm proably wrong, But I suppose it's worth a try.

-lunchmeat


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 Anonymous
Joined: 52 years ago
Posts: 0
Topic starter  

Hey lunchmeat,

It's a combo amp so that's probably not the problem. The speaker is the original one too. I'll replace the tubes and then if that doesn't change anything I'll take it to an amp tech.

Thanks for your suggestions!


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(@ricochet)
Illustrious Member
Joined: 18 years ago
Posts: 7850
 

Small signal tubes, often called "preamp" tubes, don't light up as brightly as "power" tubes that drive speakers. They don't get nearly as hot, either.

If your amp's too clean, you can bet your tubes are fine. When tubes start going bad, they distort, often unpleasantly.

The fashion up to the early '60s was for clean amps. Distortion caught on with the heavier rock of the mid 60s.

Plug some sort of overdrive pedal in front of that thing and you'll be happy as a clam. I'll recommend the Arion Tubulator pedal that MusiciansFriend has recently been selling for $9.99.

"A cheerful heart is good medicine."


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(@duffmaster)
Prominent Member
Joined: 16 years ago
Posts: 855
 

If I might Add, pre-amp tubes often determine how the amp overdrives, and various tubes will fit into one type of socket. It might have 12AY7's in it, when all it needs are 12AX7's?

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(@ricochet)
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Joined: 18 years ago
Posts: 7850
 

Here's an article with a handy graph comparing the relative gain of the types that can be readily swapped with 12AX7s: http://www.thetubestore.com/gainfactor.html

"A cheerful heart is good medicine."


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 Anonymous
Joined: 52 years ago
Posts: 0
Topic starter  

I have pretty uncommon tubes: 12AU6, 50C5, and 35W4. I replaced all 3 tubes and the amp is working a bit better but it's still too clean. I'll buy a tubescreamer or perhaps a boost pedal and then we'll see what happens :)


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(@ricochet)
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Joined: 18 years ago
Posts: 7850
 

Those are common radio tubes. The 12AU6 has a triode in it that's just like one half of a 12AX7, and the 50C5 is the power tube. The 35W4 is a half wave rectifier. Most amps/radios using one of those don't put out more than a watt or two, and many only 150 mW or so, which actually is a pretty good power level for playing around the house.

The 50C5 and 35W4 tubes are normally used in AC/DC equipment, and back then stuff was built with two-prong power cords, unpolarized. The risk is that depending on which way you happen to plug it in, the chassis of the amp will be directly connected to either the neutral wire, near ground potential, or to the "hot" wire," which gets the full 120VAC. The input jack will likely be grounded to the chassis, so if you plug it in the "hot" way, the metal parts of your guitar will be electrified. Touch a mic with your lips while you're playing, and it'll knock you down.

You can't convert an AC/DC amp to a three conductor grounded cord, but you can put on a polarized two prong plug so it'll be grounding the chassis to the neutral wire at least. The only really safe way to play one of those amps is to plug it in through an isolation transformer.

"A cheerful heart is good medicine."


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 vink
(@vink)
Honorable Member
Joined: 16 years ago
Posts: 722
 

Most amps/radios using one of those don't put out more than a watt or two, and many only 150 mW or so, which actually is a pretty good power level for playing around the house.

I need a tube amp like that (like less than 0.5W) for home use! But, unless I build one from kit or spend $500+ for a boutique amp, it looks like I am out of luck....

(Or, as I am learning from this post, I happen to luck out and find out an amp that can kill me! )

--vink
"Life is either an adventure or nothing" -- Helen Keller


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 Anonymous
Joined: 52 years ago
Posts: 0
Topic starter  

vink,

You can buy old tube amps on eBay... and you can get good ones for under $200. I don't know if you're a big fan of eBay but I am (I have to, I'm a poor student).

Anyways, there's no need to buy those famous Fender Champs amps. You can buy amps that are more obscure but still very good. I decided to buy a Harmony amp after reading the reviews on harmony central (apparently the Harmony is the poor man's Champ hehe). Other good tube amps that you can have for cheap are Airline, and they seem to be very good too. And many of them have 3 prong power cords (not original of course), so you won't get killed by your own amp.

Ricochet, by uncommon tubes I meant uncommon for tube amps. Do these radio tubes give a cleaner sound than, say, 12AX7's?
Also, does the sound change depending on how the power cord is plugged? I'm really ignorant about these things and I have no clue, but I guess I'll find out now...


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 Anonymous
Joined: 52 years ago
Posts: 0
Topic starter  

Allright so I messed around a bit with my amp... First I swaped the tubes back to the original ones and guess what, they sound no different from the new tubes. It's weird though because I remember trying the amp on the first day and it really didn't sound good at all. Perhaps the components of the amp had to "break in" and it's why it sounds better now than it did when I first received it?

So with that in mind I cranked the amp to 7 and rolled the volume knob on my guitar to 5, which is louder than what I'm used to when I play. I was actually surprised by the tube saturation at that point. So then I proceded to rolling the volume knob (on the guitar again) to 10, and then I BARELY touched the strings with my pick and wham! tube distortion in addition to a really nice sort of chyming sound. And that's with the amp volume at 7 and barely touching the strings! Let me tell you this thing is loud!

So anyways, I know what you're all thinking: crank that amp all the way up to 10 and HIT those strings! Well, that'll have to wait until tomorrow when everyone is at work...

I'm actually really excited about my amp now... I just don't understand why it sounded so crappy the first day!


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(@duffmaster)
Prominent Member
Joined: 16 years ago
Posts: 855
 

Tube saturation only comes from saturating the tube. By forcing a nice strong signal into your preamp you achieved the nice full sound of tube.

The nice thing about tube amps is that they do get loud. A 5W tube amp is close in power to a 40W SS.

If volume has to stay low at your house, but you want to keep that saturated sound get an attenuator

Who needs a signature?
I mean really...
It's almost always lyrics...
or a cliche...
or garbage about me...
Lets just save YOU from the pain, ok?


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(@ricochet)
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Joined: 18 years ago
Posts: 7850
 

Ricochet, by uncommon tubes I meant uncommon for tube amps. Do these radio tubes give a cleaner sound than, say, 12AX7's?
Also, does the sound change depending on how the power cord is plugged? The triode in the 12AV6 is just like one of the two triodes in a 12AX7. It'll be a whole lot cleaner in the amp because there's just one stage of voltage amplification, not two as in an amp using a 12AX7. As has been noted, an overdrive pedal can push that 12AV6 into clipping nicely and it'll sound fine.

You might notice a slight difference in the 60 Hz hum level depending on which way the cord's plugged in, but there's no reliable way to tell. Like I said, you can put on a cord with a polarized plug and make sure the neutral wire goes to chassis ground. Around here such a cord costs in the $5 range at the do-it-yourself stores like Lowe's and Home Depot.

"A cheerful heart is good medicine."


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(@toobmasta)
Eminent Member
Joined: 15 years ago
Posts: 20
 

12AV6? not likely, unless someone did some strange modification on this amp. Harmony never used a 12AV6 in any of their amps. This amp sounds like an H-303A. If it is, there won't be any concern about shock, it will have a power transformer. The first tube is a 12AU6. It's not a triode, it's a pentode.


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