Balanced phase inverter tube?

[Little Pigbacon]

Re: Balanced phase inverter tube?

Oh, we're not even talking about the PI anymore. We're on to biasing power tubes and "biasing" power tubes. But additional insights are certainly welcome.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

The only time you have to worry is when you have a tube, like the Tung-Sol 12AX7, which wasn't built to proper spec and can't take the voltage difference between the heater and cathode that a cathode follower circuit puts on the tube. Tung-Sols like to die there. They're OK in any other position but not the CF.

Now I'm reading of a lot of failures of Russian 12AX7's in the V3/CF spot. Some are attributing this to the "spiral filament" design. Some are modding their amps, while others are insisting that a Chinese tube is the only way to go. It's been a fun few days of researching. I almost know how tube amps work now.

 

[GilmourD]

Re: Balanced phase inverter tube?

Now I'm reading of a lot of failures of Russian 12AX7's in the V3/CF spot. Some are attributing this to the "spiral filament" design. Some are modding their amps, while others are insisting that a Chinese tube is the only way to go. It's been a fun few days of researching. I almost know how tube amps work now.

Specifically it seems to be Russian long-plates, like the Sovtek 12AX7LPS and the Tung-Sol 12AX7. The short-plates seem to be OK. A lot of guys do tend to actually like the Chinese 12AX7B in the CF position.

In my Bugera 1960 Infinium I'm running JJ ECC803S's in V1 and V3 (the PI) and I have a Chinese 12AX7B in V2 (V2B being the CF). It sounds freakin' godly. I tried a Tung-Sol in V1 before and... Meh. EH 12AX7's seem flat and uninspiring to me. The JJ ECC83S (not the ECC803S that I'm running) is dark, but that's a matter of taste.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

Specifically it seems to be Russian long-plates, like the Sovtek 12AX7LPS and the Tung-Sol 12AX7. The short-plates seem to be OK. A lot of guys do tend to actually like the Chinese 12AX7B in the CF position.

Is the 12AX7EH a long-plate?

 

[GilmourD]

Re: Balanced phase inverter tube?

Is the 12AX7EH a long-plate?

I'd have to double check but I don't believe so.

Sent from my VK810 4G using Tapatalk

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

A lot of people are pointing to the EH and related New Sensor tubes as being problematic. I think I'm going to buy a Groove Tubes GT12AX7-C that is a tested, relabeled Shuguang 12AX7A. A JJ ECC83s is supposed to be safe, as well.

 

[GilmourD]

Re: Balanced phase inverter tube?

A lot of people are pointing to the EH and related New Sensor tubes as being problematic. I think I'm going to buy a Groove Tubes GT12AX7-C that is a tested, relabeled Shanguang 12AX7A. A JJ ECC83s is supposed to be safe, as well.

Honestly, GT isn't worth the money anymore. They were great when they were the only game in town testing their tubes but pretty much every retailer now is pretty good at testing. These days GT is basically a marketing campaign and a high price. If you're going to spend more than $15 on a 12AX7 buy something NOS, like some old Mullards or something.

This is what I have:

https://www.amplifiedparts.com/products/12ax7b-china

They also have this:

https://www.amplifiedparts.com/products/7025-china

It seems as though, according to the schematic I found, that the signal goes:

V6b -> V6a -> V7b -> V7a -> V8b (CF) -> V8a (CF) -> V9b -> V9a (CF) -> V5 (PI) -> V1-4 (power tubes)

I would only recommend a Chinese tube for V8 and V9 since the these tubes (the current generation Chinese with the round getter) are pretty darn tough.

For V6 I would wholeheartedly recommend this:

https://www.amplifiedparts.com/products/ecc80312ax7-jj-electronics-long-plate

For V7 and V5... Buy a few different tubes and "tube roll" to see what sounds best to you.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

Ugh. I didn't realize V9a was also a cathode follower.

I'm thinking about tubes I can go buy locally tomorrow without having to order and pay for shipping and wait. If I'm buying two tubes instead of one, it begins to make more sense to order.

 

[GilmourD]

Re: Balanced phase inverter tube?

Ugh. I didn't realize V9a was also a cathode follower.

I'm thinking about tubes I can go buy locally tomorrow without having to order and pay for shipping and wait. If I'm buying two tubes instead of one, it begins to make more sense to order.

Yeah, I find it interesting that there's actually 3 CF stages in that amp. It does have an FX loop plus a preamp out, so that does make sense that you'd want those acting as a low-impedance buffer, plus the CF before the tonestack.

You might eventually end up like me with a box full of tubes that you've tried out in amps that will eventually end up in other amps.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

Well, I just bought two GT Shuguangs. I'm going to start out with four spare 12AX7EH. That's okay, as I do like having them around.

 

[Gone_Shootin]

Re: Balanced phase inverter tube?

That tube is a Marshall labeled Shuguang from the factory, so you just bought more of the same. And I had that very tube fail on me (before I modded it, BTW), and I'm guessing that it's the same tube that's starting to cut out when the amp gets good and warm. That position (I call it the reverb buffer tube) seems to be hard on tubes in the JVM. And about the durability of Russian tubes, they've had that reputation for a long time. That's another reason I use JJs for PIs and buffers. They seem to be a little sturdier. And in regards to buffer positions, those tubes don't effect the tone of the amp very much, if at all. So just put whatever you think will hold up a little better. But like I said, Reverb tubes seem to get chewed up in the JVM, or at least in mine.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

That tube is a Marshall labeled Shuguang from the factory, so you just bought more of the same.

The amp had all Tung Sols when I bought it on the used market. I was going to use JJ's in these two spots but there was too much conflicting information out there on which JJ -- if any -- was a good bet.

I did get two tubes, for V3 and V4 (V8 & V9 on the PC).

 

[Gone_Shootin]

Re: Balanced phase inverter tube?

The amp had all Tung Sols when I bought it on the used market. I was going to use JJ's in these two spots but there was too much conflicting information out there on which JJ -- if any -- was a good bet.

I did get two tubes, for V3 and V4 (V8 & V9 on the PC).

Oh, yeah, sorry, forgot about the Tung-Sols. As far as the JJs go, I've just been using their plain, el-cheapo, ECC83s.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

Managed to destroy a tube last night by letting one of the pins fold up underneath it. Good times.

 

[GilmourD]

Re: Balanced phase inverter tube?

Managed to destroy a tube last night by letting one of the pins fold up underneath it. Good times.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

1.) I hate the 9-pin tube sockets in the JVM.

2.) I think the pins on those GT Shuguangs are crooked and made of softer metal than I'm used to.

3.) It sounds like the GT warranty is going to cover a new tube.

4.) I want a pin straightener.

 

[JeffB]

Re: Balanced phase inverter tube?

JJ 83s works great as a CF (and I use them). I wouldn't obsess there. V1/2, PI and power tubes have much more direct affect on tone.

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

Cool. I just bought a JJ ECC83S, to have it around. For now I'll try this other GT Shuguang and see how it does. I've already got one in V4.

 

[guitfiddle]

Re: Balanced phase inverter tube?

4.) I want a pin straightener.

Get yourself a bic pen like this one, pull out the ink barrel, and use the opening to carefully straighten the tube's pin. It works...

 

[Little Pigbacon]

Re: Balanced phase inverter tube?

I've read that you can straighten pins manually that way, but I'm looking for something like this:

View attachment 77824