callling all amp nerds!

[barrymclark]

Do all the tubes in a two channel tube amp apply to both channels or are there dedicated tubes for each channel?

 

Here's the thing, I love the Vox clean. The gain channel is fine... but I'd like a bit more bite and less mud. From what I was reading, others have done this to this very amp with a great deal of success in this route.. but I am concerned about messing with the clean channel too much.

 

I am looking for a bit more of a biting gain out of the channel 2.

[kbp810]

Do all the tubes in a two channel tube amp apply to both channels or are there dedicated tubes for each channel?

 

Here's the thing, I love the Vox clean. The gain channel is fine... but I'd like a bit more bite and less mud. From what I was reading, others have done this to this very amp with a great deal of success in this route.. but I am concerned about messing with the clean channel too much.

 

I am looking for a bit more of a biting gain out of the channel 2.

Amp nerd, reporting for duty:

 

Generally speaking, the same tubes are utilized for either channel; just rather the signal takes a slightly different path through the preamp circuit.

I'm not a Vox amp expert though... some amps could work differently and I'm sure there's someone who knows better than I here (Paging Slider313...)

 

What model Vox do you have and what tubes are you running now?

[Thundersteel]

Some amps (Mesa Lonestar Special, for example) utilize different tubes for different power settings.

 

For example, at the 30W setting, all 4 tubes are used. For the 15W setting, just two tubes are used. Finally, only one tube is used for the 5W setting.

 

By the way, 5 watts is loud! My Swart is testament to that!

[barrymclark]

Amp nerd, reporting for duty:

 

Generally speaking, the same tubes are utilized for either channel; just rather the signal takes a slightly different path through the preamp circuit.

I'm not a Vox amp expert though... some amps could work differently and I'm sure there's someone who knows better than I here (Paging Slider313...)

 

What model Vox do you have and what tubes are you running now?

It is the AC50CP2. hey are stock and I have yet to crack the cabinet to see.

 

I am gonna have to at some point though. They used these cheap as hell plastic jacks and they are very loose on the cables and I want to change that out.

 

I figured while I was in there, I would address the tubes to clean up the mud a bit. This is a common gripe I hear from most about the gain channel and that a tube swap really helps here.

 

What one person did to help with the 'darkness' is put an Ei Elite in V1 and a NOS RCA in V2. In V3 and V4 he had Tung Sol resissues.

[barrymclark]

The schematic shows that there are 6 pre amp tubes.

 

The first one is at input.

 

Then it splits per channel.

 

V1b and V3a are in channel 1 (clean)

 

V2a, V2b and V3b are in channel 2 (hi gain)

 

Still trying to hunt down what the tubes in there actually are.

[kbp810]

It is the AC50CP2. hey are stock and I have yet to crack the cabinet to see.

 

I am gonna have to at some point though. They used these cheap as hell plastic jacks and they are very loose on the cables and I want to change that out.

 

I figured while I was in there, I would address the tubes to clean up the mud a bit. This is a common gripe I hear from most about the gain channel and that a tube swap really helps here.

 

What one person did to help with the 'darkness' is put an Ei Elite in V1 and a NOS RCA in V2. In V3 and V4 he had Tung Sol resissues.

Yep, I've never liked those little plastic cliff jacks...

 

Tubes sound like a good starting point, and the above sounds like a good setup! I like the Tung Sol Reissues - I bought a pair for my last build to use for the first startup tests before throwing in some RCA's (didn't want to risk potentially frying any NOS tubes)... and while there was a subtle difference between the two, they both sounded great and had a nice smooth creamy style distortion.

[barrymclark]

For the gain, I am looking for HIGH gain with as much clarity as I can get.

[kbp810]

The schematic shows that there are 6 pre amp tubes.

 

The first one is at input.

 

Then it splits per channel.

 

V1b and V3a are in channel 1 (clean)

 

V2a, V2b and V3b are in channel 2 (hi gain)

 

Still trying to hunt down what the tubes in there actually are.

Hmmm, interesting

 

Sounds like there are actually 4 (with the a/b distinguishing mode or channel)

I'm guessing of course... (haven't seen a schematic) V1 is clean, V2 must be soley for the gain channel, V3 is PI, and v4 is driving reverb (again I'm just guessing!)

[barrymclark]

Hmmm, interesting

 

Sounds like there are actually 4 (with the a/b distinguishing mode or channel)

I'm guessing of course... (haven't seen a schematic) V1 is clean, V2 must be soley for the gain channel, V3 is PI, and v4 is driving reverb (again I'm just guessing!)

The schematic is in the manual.

 

Manual

[tulk1]

There's a VOX Amps forum. Maybe they'd have some good suggestions on tubes, etc.

[kbp810]

The schematic is in the manual.

 

Manual

Looks like they give you a flow chart, but not the actual schematic - still helpful though

 

I was close! (V4 is the splitter)

 

It looks like V2 would likely have the biggest impact on your gain channel while minimalizing impact to the clean one

 

Of course Tulk1's suggestion sounds like a good idea (if you haven't checked there already)

[212Mavguy]

Looks like they give you a flow chart, but not the actual schematic - still helpful though

 

I was close! (V4 is the splitter)

 

It looks like V2 would likely have the biggest impact on your gain channel while minimalizing impact to the clean one

 

Of course Tulk1's suggestion sounds like a good idea (if you haven't checked there already)

 

Here are a few preamp tube suggestions to get more bite out of the high gain channel. Looking at the diagram, (not a true schematic, by the way) it looks like v1 and v2 are going to be your easieast tickets to what you want. The VOS (vintage old stock, used) tubes I suggest here are pretty much top tier that can be found without too much trouble or expense, likely only double to triple cost per tube compared to today's less than wonderful modern production units. Count on three out of four to be real winners. True NOS (new old stock) tubes will be much more expensive and they will need to be broken in for a couple hundred hours to sound their best. I'm speaking from the viewpoint of having collected around three to four hundred vintage tubes over the last few years.

 

For v1, put in a Raytheon long black plate, somewhere in the 1960-1962 range of manufacture. They put out a superb clean tone, nice top end detail and very full and rich sounding overall in response. They have a partial third mica to help with control of microphonics. They are often found on ebay with organ maker's logos on them, Baldwin and Schober for example...For V2, look for a 60's Amperex 12ax7 shortplate with a "delta" or right triangle in the acid etch. Those were made in Heerlen, Holland in the 60's. They provide a smooth sounding dirty tone that has the kind of bite you want, more so than their Mullard shortplate cousins from the same time period. If that does not give quite enough bite, then look for a Matsushita 12ax7 with the 45 degree flashing in the top of the bottle, they have the most treble of that tube type, and still have a full midrange and bass to them. They were made on Mullard tooling in japan, those in the know refer to them as "Japanese Mullards," very well made and long lasting tubes. In a high gain amp they will tear your face off! Another alternative to that Matsu-not-so shitty is the RCA shortplate 7025.

 

I'm talking about vintage tubes that are most definitely superior in build and tone to what is built today. They will tend to last MUCH longer than any modern production tube of the same type most of the time.

 

Finally, attention to your power tubes and particularly the bias setting will have an effect on the tone. A colder bias, somewhere in the 55-60% max dissipation rating will yield more bite to your distorted tones and brighter top end on cleans, where a hotter bias (70-75%) will bring more of a warm, fat sound that is good for lower to medium gain blues tones. That hotter bias will shorten power tube life some compared to the colder setting. For the power tubes, if you are using, look for a matched NOS pair of Siemens el34's (if el34 is what your amp uses as a tube type,) they sound WONDERFUL! Can find a pair for 130 bucks at Angela Instruments. Worth every single stinkin' penny! That tube was often found in older British Marshalls, the American imported Marshalls often used 6550's.

 

A great amp will give back hugely when pimped out in the tube department...and it's what your beautiful looking and sounding Heritage guitars truly deserve, top tier amplification for top tier guitars. There are a lot of "right" answers for your question besides what I have suggested here.

[barrymclark]

Thanks everybody!

 

I know it is definitely a mix and match game to find what truly makes you happy. The gain isn't bad, it could just use a bit more bite as you put it but, more importantly, I wanting more clarity.

 

That Vox is just one of the sickest amps I have ever heard. I get into more jazz and, believe it or not, more, as they put it, technically oriented heavy metal. For that, I need rich gain with a fair amount of clarity.

 

I know the speakers may also be adding to the mud. The Wharfedales sound great on the clean though!

 

Here is the schematic for the 100w head version. The only difference is the two extra EL34s.

[212Mavguy]

Thanks everybody!

 

I know it is definitely a mix and match game to find what truly makes you happy. The gain isn't bad, it could just use a bit more bite as you put it but, more importantly, I wanting more clarity.

 

That Vox is just one of the sickest amps I have ever heard. I get into more jazz and, believe it or not, more, as they put it, technically oriented heavy metal. For that, I need rich gain with a fair amount of clarity.

 

I know the speakers may also be adding to the mud. The Wharfedales sound great on the clean though!

 

Here is the schematic for the 100w head version. The only difference is the two extra EL34s.

 

 

You should get a lot of that clarity from the particular preamp tubes suggested alone...That's exactly why those tubes were chosen to suggest.

[barrymclark]

You should get a lot of that clarity from the particular preamp tubes suggested alone...That's exactly why those tubes were chosen to suggest.

I did find this post in another forum:

V1A- Channel 1 and Channel 2 input gain stage

V1B- Channel 1 gain

 

V2A- Channel 2 gain

V2B- Feeds the fat switch on Channel 2

 

V3A- Feeds tone controls of Channel 1

V3B- Feeds the tone controls of Channel 2

 

V4A- One side of the phase splitter

V4B- Other side of the phase splitter

[barrymclark]

Ok, after some real tooling around, I would say this is the issue I have with the gain channel. The bottom end is just unweildy. Now, I am on the second floor of my house and I know that will add bass, but it is so much so that I have to turn my bass knob down to about 1, midrange all the way down, treble and presence all the way up.

 

From what I have seen, I hear the EL34b (I see some places that it is a 'b' and others that it is just an EL34) is produced by Ruby Tubes.

[tulk1]

From what I have seen, I hear the EL34b (I see some places that it is a 'b' and others that it is just an EL34) is produced by Ruby Tubes.

Branded by Ruby Tubes. They don't make their own. Like Mesa, they buy tubes and put their logo on them. Most likely rebranded Sovteks. Barry, the easiest and least expensive swap is to start with the pre's, as suggested. You'll be amazed at what some quality tubes in that amp will do. My AC30 was supposed to come with TungSols, but were Sovteks. Installed some nice NOS tubes and that baby sparkles. Heavy as all get out, just like yours. But man, does it sing now.

[tbonesullivan]

whoa.. how did I miss this? Anyway, it depends on the design of the amplifier. Some amps have different signal paths for each channel (such as in the Fender reverb amps).

 

Most modern channel switching amps tend to share some tubes, but not others.

 

Now, most new amps these days come with what are, IMHO, crap new production tubes. Just replacing these with good new production tubes can have a profound effect on the sound. NOS or old-production used tubes are nice, but can be very pricey.

 

I've found that the best all-around new production tubes are the JJ/Tesla ECC83S and the EHX 12AX7. The Sovtek 12AX7 LP and LPS are nice but not recommended for combo amps (only heads). The Chinese/Shuguang tubes are also good.

 

Tubes to stay away from: Sovtek 12AX7A/B and even C. These are just low gain, brittle sounding bassy tubes. They don't break up well and ruin gain channels. they are ok for clean and reverb drivers but not much else. The GT 12AX7R tubes are simply rebranded 12AX7As from Sovtek.

 

These are also stock tubes in a lot of amplifiers, which is why you get such an improvement just from switching the preamp tubes out.

[slider313]

Try a GE 5751 in place of the 12ax7 for your "gain" channel.

[barrymclark]

Alrighty....

 

I pulled the tubes to see what they were.

 

The power tubes are Chinese made Ruby EL34bstr's which from what I hear Ruby is notorious for getting their hands on really cheap tubes.

 

The pre amp tubes are Tung-Sol Russian made 12ax7's.

 

The power tubes have equal glow.

 

The pre amp tubes, however, do not. The far left one has a noticable glow but you have to turn off the lights to see the glow from the others in the pre amp section. Normal? I always though they had to have a somewhat similar glow.

[212Mavguy]

Alrighty....

 

I pulled the tubes to see what they were.

 

The power tubes are Chinese made Ruby EL34bstr's which from what I hear Ruby is notorious for getting their hands on really cheap tubes.

 

The pre amp tubes are Tung-Sol Russian made 12ax7's.

 

The power tubes have equal glow.

 

The pre amp tubes, however, do not. The far left one has a noticable glow but you have to turn off the lights to see the glow from the others in the pre amp section. Normal? I always though they had to have a somewhat similar glow.

[212Mavguy]

The glow you are describing in the preamp tubes are the heater elements that go inside the cathodes. A variance in the amount of glow you are seeing from the top of the tube is inconsequential. Same thing for the heater glow in the power tubes. Remember how I earlier said that there are lots of "right" answers for your original questions? Well, one of the true amp gurus here just made a simple, excellent suggestion. GE 5751's are relatively easy to get on ebay, which, by the way is the source for most of the tubes I earlier suggested as well as what is in my collection.

 

I think they sound VERY good in high gain situations as well as their clean tones. Because the 5751 tube type was designed to be extra rugged for military use, they tend to last longer than modern production 12ax7's and are more resistant to microphonics, especially over time. The kind of tone they provide in a higher gain situation has great balance from low to high frequencies, and likely will sound noticeably better to your ears than those Russian so called Tung Sol 12ax7's, which bear about as much resemblance in build and tone to the original Tung Sol 12ax7's as generic ice milk compared to Haagen-Daz ice cream.

[barrymclark]

Thanks guys! I will definitely look into that! I also found this. What do you think?

 

I've read ALOT of threads and reviews about this amp being too muddy sounding, which I found to be true. But after viewing the schematic I realized why. The coupling capacitors between the phase inverter tube and the power tubes are .1 uF instead of .022 uF. The .1uF are used in the tweed Fender Bassman and Marshall Super Bass amplifiers, while they switched the value to .022uF for the Marshall lead amps.

 

Steve Grindrod from Marshall amp fame was key in the design of these amps and I don't know why they chose the bass amp value for this when all the others used the lead amp value. The circuit architecture of the phase inverter/power stage is the same in all these amps, except the component valus differ a bit. I've heard it said that the .1 is better for a 2x12 combo because of the extra bass, but I disagree. It's too muddy, and time and experience has shown that .022 uF works perfectly for modern/classic/British rock.

 

I bought (2) of the .022uF capacitors for $1.00 each from MetroAmps and am doing the conversion as soon as they arrive. I will let you know how it turns out. Remember: Tube amps contain lethal voltages, and mods should not be attempted by non-experienced in amp repair/modifications. Thanks!

 

He later posted:

o.k, it's been 5 months since my last post, and I only today got around to installing the .022 uF capacitors in between the phase inverter and the power tubes. It wasn't too hard of a task to do, but I made some coffee and took my time to ensure a clean job.

 

It's C16 and C35 on the circuitboard. I took before and after photos. I can send them if you'd like, but have no way to post them. How does it sound now? Way Better.

 

The muddyness is gone and it's a more useable amp now. Having said that, It still sounds like the Middle frequency needs to shift up or down a bit. A long time ago, I bought one of those Torres 5-way mid-shift kits and put it in a JCM-800 Marshall. Kind of cool, but after you tried all 5 settings you usually only used the one you liked best (the original one). The mids on the AC50CP2 sound like one of the unused settings on that kit.

 

Although it has great-sounding harmonic feedback now, the channel 2 on mine and all the AC50CP2's I heard on YouTube have that gritty overtone sound like BB's rubbing together that I'd like to eliminate. So my next little tweak will be to try to discover from the Vox schematic and some Marshall/Fender schematics what would be a more conventional value for the Mid part of the tone stack to make it sound less gritty and give tighter, clearer chords.

 

The AC50CP2 seems to be built around more of a Marshall-style circuit architecture than a Vox platform. No surprise since Steve Grindrod is mentioned in Mike Doyle's Marshall book as one of the amp designers around the JCM800 series. They had to get him to tone his designs down a little bit. This amp has all the potential to give a good mid-60's to mid-70's sound, but it's not quite there yet..

 

What do you think? Or would I honestly be spending WAY too much time trying to make the gain channel do something it doesn't want to do?

[barrymclark]

I guess the other option is I can just change out the tubes and, if I can't get the clarity I want, then get a Marshall Guv'Nor or something so I don't have to use the Fat switch and mud out the bottom end.

[tbonesullivan]

Tung Sol reissue tubes have almost no filament glow when compared to other tubes. only the sovtek LPS has less glow, due to the spiral filament.