M8080 Replacement LP260MSE Monoblocks

[gregborowski]

So I have a mint pair of LP260M SE mono blocks and the right channel is throwing off the paper tearing / light popping sound that I believe is attributed to a failing Mullard M8080 tube. I can't seem to find anyone with these tubes in stock. Does anyone have a recommendation for an equivalent tube? I would like to find a pair and keep a single as replacement in case of another failure.

I emailed CJ a week ago but never heard back. I'd also be interested in a pair of 6N30P tubes as well. Those are also seemingly hard to find.

[Joe Appierto]

Upscale Audio carries both the Sovtek 6H30 and EH gold pin 6H30.

Tube World has two single M8080 tubes available. https://tubeworldexpress.com/collections/preamp/6100

[gregborowski]

Wow thank you. Not sure how I missed those. I assume the 6H30 is equivalent to the 6N30?

[Joe Appierto]

You're welcome. The 6H30 and the 6N30 are exactly the same tube. One is in Cyrillic (6H30) and the other in English (6N30).

[gregborowski]

Thanks Joe, orders are in.

[Truth71]

FWIW, I THINK 6C4 is an acceptable substitute for M8080, as well as CV4058

[Big Dog RJ]

Yes that's correct on those Mullards M8080 tubes: 6C4 and CV4058 are the correct type. In the case of Mullards they're just referrer to as M8080.

I always get my M8080 tubes from Watford Valves in the UK, price was around 16 pounds, about $32 AUD (Aussie dollars). My CJ techie also had other brands, such as RCA and Ratheon but the Mullards were amongst the best. Many years ago, Matsushita factory in Japan made these tubes but now classified as NOS, and rare NOS this is going back to the 60's and 70's. Since then Matsushita ceased production. The Mullards are still available and come in reissue new production but do have premature failures on certain batches. The key to success is keep sourcing these tubes until you find a reliable pair & brand, then just stick with that! And of course keep a few spares.

***Note*** since these are small signal tubes, mainly used in the input gain stage, they generally should last over 6 - 7yrs with no issues.
Therefore, two pairs of spares will last you a lifetime! Unlike high powered Output tubes, which need changing at least once in 3 to 4yrs of normal operation.

The 6N30P or 6H30PI (exactly the same) are generally available from Sovtek or EH (electro harmonix). Aa far as I'm aware, no issues with stock on these tubes. There are several suppliers, Valve Store (Aus), Tube Depot, the Tube Store, Upscale (a bit tricky to deal with...) and Watford Valves UK. My last order on these 6H30PI's were placed directly from CJ, which were the Sovtek gold pin version. The others were sourced from The Valve Store, included the EH brand but standard silver pins version. I preferred the Sovtek gold pins in my CJ preamp.

Cheers, RJ

[SolderSlinger]

@Big Dog

"The Mullards are still available and come in reissue new production but do have premature failures on certain batches." Is there a Mullard M8080 reissue? I searched and can't find a source.

I've considered buying a pair of LP260MSE but the M8080 scares me off. I talked to CJ about 4 years ago about the M8080. At the time there was stock but only "amp grade". Not quiet enough for a preamp. My listening room is very quiet. I can hear noisy amp input tubes.

Availability of the M8080 is a real issue. Here's an Audiogon Forum post dated 5-30-23 "I have a CJ PV14L that has 2 x m8080's - it seems the Mullards are the way to go but after contacting CJ [ Took 10 days for a call back ] they were not much help - suggested I sell the pre amp ! no tubes from them available ...ugh"

[Big Dog RJ]

Mmm... now that's a worry. I've still got a few spares but not too many though. Looks like I'll have to source from our local grumpy tube supplier, he always works something out.

I've been contact with Watford Valves UK, still have stock of Mullards. Not sure whether these are Mullard reissue but I'm thinking more NOS type. Bit risky due to sudden failures but who knows. No wonder JF switched over to the 6922 variant, widely used and plenty of stock!

Cheers, RJ

[gregborowski]

Quick update. I replaced the M8080 in the right channel with a NOS RCA 6C4. Good news is the paper tearing sound has disappeared. The bad news is the infrequent pops in the right speaker are still there (weird as I thought those two things were related). It happens somewhat randomly about every 3-5 minutes. It's loud enough to startle. The KT120s on the channel are all good and recently biased within the last 10 hours of use.

So by chance I wondered if the pops were being generated by my preamp. I have an original Shindo Laboratory Monbrison preamplifier. I switched the outputs and sure enough, the pops moved to the other speaker. So the CJ amps are all good. Sounds like I have a bad tube in the right channel of the Monbrison. Is there a Shindoowners.com support group?

I'll take the Shindo out of service for now and bring up my PV-5 (restored by Bill Thallman 2 years ago).

[admin]

Glad some of the issues are solved. If the popping is changing sides with the L/R interconnects between the preamp and amp switched, it would signify a preamp issue (or source for that matter). You may just want to swap the source interconnects to be 100% sure but most likely a preamp issue.

One last thing with intermittent but reliable pops,.. it could potentially be static discharge. I only mention this as I get a lot of static in my room during the winter time. The air and very dry in New England during the winter and I get static discharge when I touch my equipment. On the off chance that this is what is causing the pops, you can try putting a humidifier in the room and see if that helps at all.

[AnotherJohnson]

In my experience with CJ, the twin triode driver tubes in the amp can create popping as their life begins to end. The tearing sound is usually a twin triode in the preamp.

It is hard to troubleshoot an intermittent phenomenon. Sometimes the easiest thing is just refresh all the driver tubes.

[jeffreybehr]

I had an MET1 years ago and researched--that means buying MANY and testing-as-best-I-could--MANY 6C4s..The biggest difference I found was in microfonics--very few had none or virtually none--and some hurt my ears as the preamp clicked on--I was sitting close to the speaker.. I suggest U buy a bunch of inexpensive 6c4s on eBay and test them.

FWIW, I just e-mailed Brent Jesse to see what he has.

[admin]

I have 6C4's in my PV-14L and the first thing I had to do when got the unit (used, not new) from the seller was to replace the tubes. It went well beyond microphonics to clear distortion, but I wonder if these are just very sensitive tubes by nature. Luckily they are inexpensive.

[Big Dog RJ]

Admin mate,

You also have these tubes in your ART monoblocks. They're used in the Input gain stage. CJ preferred to use this tube primarily as the Input gain on a few selected amplifiers and preamps but later on changed over to the 6922 variants, which is widely used in current production.

I'm thinking must be something to do with production and stock, otherwise there was no apparent reason to discontinue the use of this tube. The M8080 Mullards are highly musical. Just love them.

Cheers, RJ

[admin]

Yup, the M8080 is in the ART monoblock input stage. I don't know if it's that specific tube or the combination of everything but I sure like it! I'm not exactly sure where there are made, I presume a lot of the production is in Russia so that doesn't bode well for supply.

[AnotherJohnson]

Yup, the M8080 is in the ART monoblock input stage. I don't know if it's that specific tube or the combination of everything but I sure like it! I'm not exactly sure where there are made, I presume a lot of the production is in Russia so that doesn't bode well for supply.

He used 6550s and 6922s in the LP275M.
When he upgraded mine to run KT120s, he kept the 6922s.
He must have consciously chosen the M8080 in preference to the 6922 for the original ART amps.

[SolderSlinger]

My $0.02 is at the time of introduction the LP275M with 6922's was too big of a step away from the sound of the Premier 8. CJ folks weren't ready for a neutral amp. The ART mono with the M8080 (single triode 12AU7) took a small step back from the LP275M, and towards the Premier 8. I personally like the sound of the 6189/12AU7 input tube. It's used in the Classic 60SE, LP125sa, and ARTsa. The M8080 is used in the LP260M, and ART mono.

Now if someone would make a tube adapter that allows fitting a 6189/12AU7 in a M8080 socket; it would open up the choice of tubes.