Noob tube question: Please Help!!!

[6_6_6_1_syn]

I'm sorry to be such a noob, but I have a few extremely basic questions that I'm almost embarrassed to ask. What is a preamp tube, and what is a power tube? What are output and input tubes? Also what is a preamplifier? Is a preamplifier like an amp head or rack piece with that function, or is it something totally different?

Thank you!

 

[Russ]

Ok first things first. A preamp is the section of the amplifier that receives the input signal from your guitar via the cable. This preamp then will boost your signal and allow you to adjust its frequencies as necessary before sending it to your power amp. The preamp is often referred to as the input stage of your amp. Often amp manufacturers make preamps separate from power amps and make them both rackmountable so you can interchange the two parts with parts from other manufacturers or with their other designs. Part of the preamp in a tube circuit is a preamp tube. Typically these tubes are mini 9 pin (noval) tubes. In guitar amps they will most likely be 12ax7/Ecc83/7025, 5751, 12at7, or 12au7. These tubes can also be referred to as input tubes when speaking generally. In a Dual Rectifier these are the five little tubes closest to the actual front of the amp and furthest from you when looking at the rear of the amp.

Power amps in a tube circuit typically have power tubes. These can be generalized as output tubes though usually there is some sort of phase inverter that usually requires some sort of balanced preamp tube to drive the power tubes. Power tubes are typically much larger than preamp tubes and are typically of some sort of 8 pin (octal) design though you may encounter tubes of other design like an EL84. In a Dual Rectifier these are the four large tubes to the left when looking at the rear of the amp.

In the case of a head or a combo amp all the components and tubes of both a preamp and a power amp will be in the same enclosure.

Before you repost and ask what a rectifier tube is I will answer that in a really easy way. A rectifier tube rectifies the signal, thus "rectifier". It changes the way the amp presents its tone. Because there are different rectifiers, you can choose between them if you have a notion to change the way your amp sounds. Different rectifiers will have various effects on your amp. Some are more saggy then others. The Diode option on the Rectifier amps is the tightest sound you can get from them because you are not using a tube for rectification. These tubes are 8 pin (octal) design also. Do not confuse them with power tubes. In any tube rectified amp you will have one rectifier tube per pair of output tubes. In a Dual Rectifier they are the two large tubes located at the far right when viewing the back of the amp.

 

[stokes]

"Before you repost and ask what a rectifier tube is I will answer that in a really easy way. A rectifier tube rectifies the signal, thus "rectifier". It changes the way the amp presents its tone. Because there are different rectifiers, you can choose between them if you have a notion to change the way your amp sounds. Different rectifiers will have various effects on your amp. Some are more saggy then others. The Diode option on the Rectifier amps is the tightest sound you can get from them because you are not using a tube for rectification. These tubes are 8 pin (octal) design also. Do not confuse them with power tubes. In any tube rectified amp you will have one rectifier tube per pair of output tubes. In a Dual Rectifier they are the two large tubes located at the far right when viewing the back of the amp."

A rectifier doesnt rectify the signal.Has nothing to do with your signal at all.A rectifier rectifies the ac voltage from your PT to dc voltage for your B+ power.The only effect it has on your tone is,depending on the internal resistance of the particular rectifier,will drop some volts in your B+ supply,the more volts that are dropped in the rectifier,the more sag you will experience.There are other amps besides the Dual Rectifier that use 2 rectifier tubes.Not all rectifiers are octal,although they are the most common,there are older amps that used 9 pin rectifiers as well as the now almost extinct 4 pin "83" rectifier.

 

[tommyhawk13]

Whoa, fellas, Let's not scare the guy!

A preamp can be just what Russ said, or it could be 1 amplifier plugged into another amp, or power amp. I used to do that & it was a great way to get that perfect sound at whatever volume I wanted.

OK, this is basic, and I'm sure someone will correct me If I'm wrong.
Mesa Boogies are known for getting most of the sound out of the preamp section, but this is not the norm for older tube amps.

You used to have to crank up your tube amp to a certain volume to get distortion. This is when the power section is pushed to its limits & starts to "break up". This is also called overdrive.

Even though the preamp section makes most of the tone, the power section still plays a part. Some tubes have more bottom end and clarity, while others "break up" sooner. The 6l6's have more headroom than the EL34's, and the little EL84's break up real soon. I'd go out on a limb and say that the EL84 powered amps have the most drastic effect on an amp.
Vox AC30, Mesa 20/20, and some of the Peavey Classics are EL84 amps.

 

[stokes]

Cranking an older Fender type amp is pushing the preamp to its max,think of the volume control on these amps as your preamp gain,this in turn will push the output tubes into "overdrive"or "saturation" if the power tubes are biased properly.In a Mesa style amp,you have a master volume which is just after the preamp so you can push your preamp into overdrive and lower the signal going out to your power tubes,getting distortion at lower output volumes.Mesa type amps,when used stock,have very little power tube saturation or distortion,all your distortion is produced in the preamp,while the output is biased for max clean output and power.

 

[6_6_6_1_syn]

Thanks for all the help , but I still have a couple of questions. If there is an EQ built into your amp, will it be placed between the preamp and power amp, to alter the signal produced by the preamp? Should I know all of the tube types and what kind they are, or is that something I could look up if I plan on replacing the stock tubes?

 

[stokes]

Which amp are you talking about?

 

[6_6_6_1_syn]

I guess nothing specifically. Wouldn't there be a general setup?

 

[stokes]

Tone stacks and EQ's can be placed in different stages of the preamp.

 

[Elpelotero]

The EQ comes before the preamp and then the preamp goes into the poweramp. The preamp is where the tone gets shaped.

However, if you want to add more EQ via a pedal or what not in the effects loop, it is best to place it between the preamp and poweramp via the effects loop.

you don't really need to learn all the tubes now...many of us here know very little about the tube brands save for a select few. it's a whole other massive topic all on its own. most people just plug in wht sounds good to them given their current mood.

 

[6_6_6_1_syn]

Thank you very much, everything is starting to make sense now! I was planning to buy a sonic mazimizer and noise gate, and its all making sense now!

 

[Russ]

"Before you repost and ask what a rectifier tube is I will answer that in a really easy way. A rectifier tube rectifies the signal, thus "rectifier". It changes the way the amp presents its tone. Because there are different rectifiers, you can choose between them if you have a notion to change the way your amp sounds. Different rectifiers will have various effects on your amp. Some are more saggy then others. The Diode option on the Rectifier amps is the tightest sound you can get from them because you are not using a tube for rectification. These tubes are 8 pin (octal) design also. Do not confuse them with power tubes. In any tube rectified amp you will have one rectifier tube per pair of output tubes. In a Dual Rectifier they are the two large tubes located at the far right when viewing the back of the amp."

A rectifier doesnt rectify the signal.Has nothing to do with your signal at all.A rectifier rectifies the ac voltage from your PT to dc voltage for your B+ power.The only effect it has on your tone is,depending on the internal resistance of the particular rectifier,will drop some volts in your B+ supply,the more volts that are dropped in the rectifier,the more sag you will experience.There are other amps besides the Dual Rectifier that use 2 rectifier tubes.Not all rectifiers are octal,although they are the most common,there are older amps that used 9 pin rectifiers as well as the now almost extinct 4 pin "83" rectifier.

Ok, I am sorry if my rectifier information was somewhat misleading regarding "signal" v. voltage. It was not intentional. I was merely trying to give an idea of what it does. I am in no way trying to start a pissing contest nor am I about to start backpeddling here for anything. In reference to the Dual Rec, I chose that particular amp as a reference because it happens to be the most common of the Rec line. Obviously, a Triple has three rectifier tubes. Curiously enough, the Single only has diode rectification. Being that our friend is new to Mesa and tube amps I was just trying to help him get comfortable without getting into the really technical side of things that may cause him to lose interest or be intimidated by parts. I myself know that the octals are not the only rectifiers in existance. Personally, I love the look of the big 83. I have one in my tubetester too. I might swap that out for a diode type replacement though because 83's are becoming harder to come by and I think that the replacement will do just as well if not better in that application. I am intrigued by old tube applications and have a small collection of tubes that are functional though the gear and the tubes themselves have found obsolescence.

 

[stokes]

Russ,I did not intend to start any pissing match at all,sorry if it sounded that way,just trying to RECTIFY some misinfo.Be careful switching that 83 to solid state in your tester,it could foul up your test results,I picked up a NOS 83 on ebay for $3 with a 4 pin socket included,the shipping was more than the item.They are out there,just gotta do some searching.I see them at hamfests quite often,for practically nothing.I was at one this past weekend and a guy I see at a lot of these flea markets had a couple.Next time I see him I'll grab one for you if you want.I got a nice pair of 7581A's from him for $35,didnt ask what he wanted for the 83's but I dont think he would ask too much.I think there's another hamfest in my area in June.Let me know what you are willing to spend for one,and if I go I'll see what I can do.

 

[Russ]

A pair of 7581A's for $35? They weren't NOS were they? I think I would have to check my shorts if that was the case.

The reason I wanted to swap to a SS rectifier in the tester is because I can't check the rectifier in the tester for some stupid reason. They didn't supply any socket for it and I don't think it is wired too either. People that I have asked about that BK say that it just can't test the 83. I was told that the SS would make for more reliable and consistent readings. I am assuming that the 83 in it currently is ok because I get the same readings on the same tubes that I have as reference tubes when I test them. I get different readings on the rest of the tubes I test also but they are consistent if retested even on different days so I am assuming that the rectifier is fine because it seems to give consistent readings on the same tubes when retested. It wouldn't be a bad idea to at least have a backup in case of failure though.

Do you have experience with the 83 SS replacement rectifiers?

 

[stokes]

Yes,they are NOS Tung-Sols,but I made a mistake,they arent 7581A's,they are 7581.The A's are a pair of RCA's I got last month on ebay.I am a NOS snob,I dont use any current productions at all.Between me and my 2 sons we have 18 amps all with various NOS tubes,and I have a stash of about 150 or so spares.Most of them come from these hamfests,and I have culled out quite a few marginal and bad tubes,I only keep the ones that test new or close.Heres one that'll make you check your shorts.About a year or so ago I saw a guy with a quad of clean,new looking RCA Blackplate 6L6GC's.He said he got them new in the early '60's and since he never got to use them he had to get what he paid,which he thought was around $25,I was more than happy to give him $30.There are alot of tubes out there,just gotta do some leg work.As for the 83 solid state sub,I have never used one,and I base what I said on common "lore".I have always heard and read that it is not advisable to use a ss in place of a tube in a tester,they raise the voltage and throw off the tests.But I guess when you consider the age of most testers,it may not make that big a deal.I may have an extra spare 83,I'll have to go thru my boxes and see.I got them for backups for my Hickock 550,which I havent used since I picked up a nice Weston a couple years ago.If I find I have an extra one,I'll PM you and see if you want it.

 

[Russ]

Hey thanks. That is really kind of you.

The deal on the RCA 6L6GC's was a steal too. I think I might have to check out a Hamfest. A friend told me about one a couple years ago and I thought that it would be a waste of time. I should have gone. I'll have to keep my eyes open for a Hamfest. Do they advertise these things? I think the one he was telling me about was either Downtown or at the fairgrounds.

How does your Weston unit compare to the old Hickok? I take it you like it better because you said you aren't using the Hickok anymore since getting it.

 

[stokes]

The Weston is great.The 550 was really old,and I had to make an adapter to test AX7 type tubes.The Weston has a good rep,its the 981-3.Its came from IBM and had been in storage for years,a friend of mine that worked for them at the time had one of the old techs there calibrate it for me and I got it for nothing.It also has 2 extra nine pin sockets that look like they were added at the factory,as well as a nine pin pre-heat socket.It was apparantly used exclusively for nine pin tubes.Check your PM for hamfest info.