Tubes for a Peavey 6505

[GrimmDixie]

I'm wondering if Groove Tubes 6L6R (aka 6L6B) will be a correct match for my 6505 combo. Help?

 

[LerxstLee]

What are the numbers on the tubes that came with the amp. Do you have those.
They might use PC/GM or PC/TC numbers. There might be a simple number for ex. 5.
With those numbers I can usually translate that into the proper groove tube number for you,
the choice of tubes I am not going to get involved with. I like Pepsi products, and god
forbid I tell you a brand to put in there, then I have to hear OMG pepsi blah blah, it has to be coke.
Yes , I am exagerating but opinions have turned into verbal warfare, I would love to help, and
will do that if you can tell me the tubes you are replacing. Yes, I can send you to someone
to put bias mods in for you so you can use, virtually any tube rating there is, yet, if you are happy with
your amp, and it has served you well,I can estimate the tube rating you need. You can take the brands to others.
/cheers

 

[94Tremoverb]

I'm pretty sure the 6505 has adjustable bias - I think the last one I worked on did (although I may be confusing it with a Valve King) - but stupidly, the test point is for the bias voltage, not the tube current, so it gives no indication of whether the tubes are running correctly or not. If I owned one of these amps I would certainly mod it so the test point was useful. Without that, you'll need to use some sort of test kit which goes between the tube and the socket.

Even if it's not adjustable, Peavey's stock bias setting (like Mesa's) is pretty conservative, so more or less any 6L6 should run OK.

 

[GrimmDixie]

Even if it's not adjustable, Peavey's stock bias setting (like Mesa's) is pretty conservative, so more or less any 6L6 should run OK.

I don't think the bias is adjustable (fixed bias???). So I'm just gonna try 'em out. All that other stuff y'all are talkin' about is like Norwegian to me. And I certainly don't want to argue about what brand tubes are best (I've read the arguments here). I've got 6505, and I've got Groove Tubes to put in it. Simple as that. If that offends you, sorry. Thanks for the info!

 

[LerxstLee]

You don't offend me in the least. I would much rather have someone say, this is my experience, I have
these tubes and I am giving it a try. I know little about peavey amps, had an original 5150-2X12 combo,
but that was short lived. If they are fixed bias and around the mid you should be fine. The way I have
been getting tubes from a few merchants lately, I would trust groove tubes numbering system, along
with their tubes and tests, second to mesa's.
Post and let me know how they work out.

 

[GrimmDixie]

Ok, the tubes in my 6505 are Ruby 6L6GCM-STR. The ones I want to put in are Groove Tubes 6L6R (aka 6L6B), and they are rated at 4 (normal distortion). Are they compatible? How will they differ (in sound) from the Ruby's? Any idea?

 

[GrimmDixie]

Peavey's stock bias setting (like Mesa's) is pretty conservative

What do you mean by "conservative"?

 

[LerxstLee]

I would say, tube current right in the middle. Mesa tube specs, or groove tube spec #s4-5-6

 

[LerxstLee]

Ok, the tubes in my 6505 are Ruby 6L6GCM-STR. The ones I want to put in are Groove Tubes 6L6R (aka 6L6B), and they are rated at 4 (normal distortion). Are they compatible? How will they differ (in sound) from the Ruby's? Any idea?

Not a clue how it will sound. Yet I am interested in what your opinion is.
Let us know what you think.
/cheers

 

[thunda1216]

In my experience, most venues will not allow me to turn my amp up enough to achieve power tube breakup. It's just too loud with a 4 6L6 amp. Very little tonal difference that I have noticed from brand to brand, even NOS.

 

[94Tremoverb]

"Fixed bias" does not mean it's non-adjustable. This is a big source of confusion. "Fixed bias" means that the bias is fixed with a separate DC voltage supply, and this is the only type that *can* be adjustable normally. The other kind is "self bias" AKA "cathode bias", where the bias voltage is generated by the current passing through the tubes themselves and is almost always non-adjustable.

So really there are three types of bias: cathode (self) bias, adjustable fixed bias, and non-adjustable fixed bias. The difference between the two types of fixed bias is only due to the presence or otherwise of an adjustment pot/trimmer.

Certainly at least one Peavey 100W head I was working on recently had a trimmer - but sorry, I can't remember if it was a 6505 or a Valve King or both! They were both in the shop on the same day - I'm afraid I was not paying a huge amount of attention and my short-term memory is not quite what it once was. Whichever it was, the test point was definitely for the bias voltage and not the tube current, which is practically useless. The trimmer was on the top of the chassis inside, not the back by the way.

"Conservative" bias setting means a nice moderate value, neither too hot nor too cold, but if anything a bit on the cool side. This makes sure that almost any tube will run *safely* (ie not too hot, potentially causing tube failure and if you're really unlucky damaging the amp), but not necessarily for the best tone, since some tubes may run a bit too cold. Personally I find cooler settings very often sound as good or better anyway, and that the current fashion for hot bias is not always desirable or necessary.

The odd thing is that most cathode-bias designs, while also not adjustable, frequently run the tubes (especially EL84s) far too hot, and that's one reason EL84s are usually thought to have a short working life. It *is* possible to make cathode bias adjustable, but it needs an expensive high-power pot, so it's very rarely done.

 

[GrimmDixie]

Ok, I switched the Ruby 6L6GCM-STRs with the Groove Tube 6L6Rs. I played it last night (at high volume), and I really couldn't tell the difference. They seem to be operating just fine, but I heard no real difference. Still the same shrieking and squealing at high gain settings as before. :lol:

 

[LerxstLee]

There is also grid leak bias which was used on some preamp tubes of a very few designs in the early '50s.
I do not believe anyone uses grid-leak designs any longer.
All preamp tubes are cathode biased well except the very few who even put a pot on pre-amp tubes./wink
An amp that is cathode biased power tubes will have a resistor from cathode to ground.
Cathode-biased power tubes are generally not as loud as fixed bias amps, that said they do seem I.M.H.O. to possess
a 'singing" quality with lots of sustain. Keep in mind that cathode-biasing is self-adjusting in pre-amp tubes, it is
not always the case with power tubes biased the same way, as they draw considerablly more current.
Your cathode biased amp can be biased in two ways which I am familiar with, thus hold your fire on cathode bias
is almost always non-adjustable.
(1) you can simply monitor the current and try different value cathode resistors until the "appropriate current is achieved.
If the plate current is too low, a smaller value cathode resistor is used, and if the plate current is too high, a Larger value resistor is used. You may even have to use two resistors to get the excact resistance. If you only have one pair of output
tubes to work with this is a great alternative to get to your great tone bias voltage.
(2) Is to simply substitute different pairs of matched tubes to find out which set will bias properly with the current & voltage of the amp you are dealing with.
As a rule, cathode-biased amps like more current than fixed-biased, 50 to 70 m.a. is not uncommon especially
in single ended amps. Many cathode biased amps ended up on those late 60's through the '70s recordings, where
you sit back and love the sound of that Lead "he just played".

 

[LerxstLee]

Ok, I switched the Ruby 6L6GCM-STRs with the Groove Tube 6L6Rs. I played it last night (at high volume), and I really couldn't tell the difference. They seem to be operating just fine, but I heard no real difference. Still the same shrieking and squealing at high gain settings as before. :lol:

You may want to look at the preamp section, I am almost certian you are overdriving the preamp tubes.
Preamp tube distortion can be a very "ugly" sound. I would say alot of players would rather crank a
nice old marshall, if they only could. That was the problem with non "master volume" amps. The sound
police were all over us once the '80s came around. At least that was my experience.

If the problem was squeeling with high gain settings on high gain amps at High volume is almost always in my experience,
the result of using high gain at high volumes on a high gain amp.
If you are cranking this amp, can you get a "good" sound without driving the preamp so hard?
Try cutting back on the gain. An example I can give you is when I play at lower volumes I tend to bump up
my gain, and at louder volumes I cut the gain back. One of the never ending problems is getting a great sound
out of amps that are no longer utilizing the power tubes for the distortion at high volumes. Other wise I would
still have my early '70s small box 50watt Marshall, that i.m.o sounded so great, yet it had to be too loud to
sound that good. I sold it, only to be sorry ever since. Now with a good part of the distortion coming from the preamp
"gain" section, the power tubes no longer do the much of the work of distortion. If I peg the gain on my road-king
using channel 3 or 4, I can't really get any volume out of it without feedback or squeeling. It is actually unusable with
the gain used over 1:00. I prefer to run the gain at no more than 9:00 and the master as high as I can get it. Yet if practicing I cut back the volume and bump up the gain.

 

[LerxstLee]

There is also grid leak bias which was used on some preamp tubes of a very few designs in the early '50s.
I do not believe anyone uses grid-leak designs any longer.
All preamp tubes are cathode biased well except the very few who even put a pot on pre-amp tubes./wink
An amp that is cathode biased power tubes will have a resistor from cathode to ground.
Cathode-biased power tubes are generally not as loud as fixed bias amps, that said they do seem I.M.H.O. to possess
a 'singing" quality with lots of sustain. Keep in mind that cathode-biasing is self-adjusting in pre-amp tubes, it is
not always the case with power tubes biased the same way, as they draw considerablly more current.
Your cathode biased amp can be biased in two ways which I am familiar with, thus hold your fire on cathode bias
is almost always non-adjustable.
(1) you can simply monitor the current and try different value cathode resistors until the "appropriate current is achieved.
If the plate current is too low, a smaller value cathode resistor is used, and if the plate current is too high, a Larger value resistor is used. You may even have to use two resistors to get the excact resistance. If you only have one pair of output
tubes to work with this is a great alternative to get to your great tone bias voltage.
(2) Is to simply substitute different pairs of matched tubes to find out which set will bias properly with the current & voltage of the amp you are dealing with.
As a rule, cathode-biased amps like more current than fixed-biased, 50 to 70 m.a. is not uncommon especially
in single ended amps. Many cathode biased amps ended up on those late 60's through the '70s recordings, where
you sit back and love the sound of that Lead "he just played".

The cathode is pin 8 on 6v6 and 6l6, it is pin 3 on el84s.

 

[GrimmDixie]

OK, yeah. It's not that there's anything wrong with the 6505, or that I'm not pleased with it. I just wanted to do a little experimenting (plus, I've had the amp for three years and I thought it might be time to replace the tubes). I also have a Mesa Stiletto Trident which squeals and shrieks when the gain is set high at loud volumes. Am I right in thinking it's just the nature of a tube amp? Anyway, I can fix all that with a noise gate.

 

[LerxstLee]

There is also grid leak bias which was used on some preamp tubes of a very few designs in the early '50s.
I do not believe anyone uses grid-leak designs any longer.
All preamp tubes are cathode biased well except the very few who even put a pot on pre-amp tubes./wink
An amp that is cathode biased power tubes will have a resistor from cathode to ground.
Cathode-biased power tubes are generally not as loud as fixed bias amps, that said they do seem I.M.H.O. to possess
a 'singing" quality with lots of sustain. Keep in mind that cathode-biasing is self-adjusting in pre-amp tubes, it is
not always the case with power tubes biased the same way, as they draw considerablly more current.
Your cathode biased amp can be biased in two ways which I am familiar with, thus hold your fire on cathode bias
is almost always non-adjustable.
(1) you can simply monitor the current and try different value cathode resistors until the "appropriate current is achieved.
If the plate current is too low, a smaller value cathode resistor is used, and if the plate current is too high, a Larger value resistor is used. You may even have to use two resistors to get the excact resistance. If you only have one pair of output
tubes to work with this is a great alternative to get to your great tone bias voltage.
(2) Is to simply substitute different pairs of matched tubes to find out which set will bias properly with the current & voltage of the amp you are dealing with.
As a rule, cathode-biased amps like more current than fixed-biased, 50 to 70 m.a. is not uncommon especially
in single ended amps. Many cathode biased amps ended up on those late 60's through the '70s recordings, where
you sit back and love the sound of that Lead "he just played".

The cathode is pin 8 on 6v6 and 6l6, it is pin 3 on el84s.

YES, #2 is not adjusting the bias in any way, it is a simple way to avoid changing resistors assuming you have
some matched pairs of tubes around.

 

[LerxstLee]

OK, yeah. It's not that there's anything wrong with the 6505, or that I'm not pleased with it. I just wanted to do a little experimenting (plus, I've had the amp for three years and I thought it might be time to replace the tubes). I also have a Mesa Stiletto Trident which squeals and shrieks when the gain is set high at loud volumes. Am I right in thinking it's just the nature of a tube amp? Anyway, I can fix all that with a noise gate.

I am not sure it is the nature of tube amps. Solid state will feed back, but do not go into the
pre amp tube squeal. That said, I am not sure that a Non master volume or a Non gain amp will have preamp
squeal, they will feed back when cranked but you will not overdrive the preamp tubes unless you have something
overdriving your guitar signal in the chain like a gain boost pedal or the like.
If you are trying to experiment with different tubes to affect the tone, I am not going to get into
the this tube is better than that tube but I will give you my opinion to the simples way to start with
a high gain amp, that would be trying some lower gain preamp tubes, I do not know the layout of those amps,
but for an example, if in my road king I wanted to lower the gain in channels 3 and 4, I might change tube
V2=triode 1=s 3rd gain stage channels 1+2/triode 2=s same for channels 3=4
V3=triode 1=s 4th gain stage channel 3&4/triode 2 is the tone stack driver

I would probably try a lower gain tube in V2, perhaps a 12az7 output (60)or a 5751 output (70). I would also try a 12at7 output (60),but some will say it lacks tone and has higher current so it may not be suiteable. I will leave it at that.
12aZ7s are found cheap as alot have little idea to its potential and very little information can be found on this tube, and
it does not have the current "problems" some associate the 12at7s with.
/cheers

 

[94Tremoverb]

I should really have said bias methods "that are used in guitar amp designs". I don't actually know of any that have adjustable cathode bias, even though it's easily technically possible, and there may well be some. I wouldn't count resistor replacement as 'adjustment', although you can do it to either fixed or cathode bias in the same way as you can mod anything. I also don't know of any designs in the modern or even reasonably vintage era that use grid-leak bias. But there *are* some modern amps that use fixed-bias preamp tubes, surprisingly! Look no further than some Mesa 20W amps - the Studio 22 and Subways for certain, there may be others - although it is only the phase inverter that's done that way.

Squealing and shrieking at high gain and volume settings will either be microphonic preamp tubes, or more likely microphonic guitar pickups. Or if you're really lucky, your girlfriend.

 

[LerxstLee]

Notice how you pick and choose your comments.

In my post I clearly indicate grid leak was used in the early '50s thus, you point out, "I don't know any designs in the modern or ect.
Clearly early '50s would leave out modern or early vintage. Mute point.

Yet you also choose to comment on the cathode bias on preamp tubes, where I said all.
Some do have fixed bias. Thanks for the info. Point taken.
/cheers