Mesa Dual Rec... Run it without the 5U4 ?

[EtherForBreakfast]

Grrr. Received a Dual Recto today and the fucking thing is nothing but shattered glass everywhere. Preamp tubes are fine, but the power and recto tubes are decimated.

I have a pair of 6L6 JJ I am going to throw in at the 2 outer sockets which will be fine, but can I set the switch to diode recto and run it with NO rectifier tubes?

 

[Matt Crooks]

I have heard yes, but not tried it.

 

[EtherForBreakfast]

In case anyone is wondering I just went ahead and held my breath and did it... works just fine with no recto tubes in there as long as the switch is set to diode.

Bummer is that the thing arrived with 6 shattered tubes. Good part is that UPS will be buying me a new quad of 6L6 and 2 new 5U4.

UPS sucks. I swear they must have done an Ace Ventura on this thing.

 

[FULLMETALSPEEDO]

I swear they must have done an Ace Ventura on this thing.

HDS Comin thru!!! GOTTA PACKAGE PEOPLE!!!!!

 

[JeffTD]

I will never ship UPS again - last month, they destroyed the headbox of a Single Rectifier I shipped. I'm still waiting for them to buy me a new one.

That said, as you found out, running it on the diode mode without the rectifier tubes in is completely fine. Just remember when running half the power tubes to also half the impedance, as with 2 tubes pulled, the 8 ohm jack puts out 16 ohms, 4 puts out 8, etc.

 

[Familia><Publica]

I will never ship UPS again - last month, they destroyed the headbox of a Single Rectifier I shipped. I'm still waiting for them to buy me a new one.

That said, as you found out, running it on the diode mode without the rectifier tubes in is completely fine. Just remember when running half the power tubes to also half the impedance, as with 2 tubes pulled, the 8 ohm jack puts out 16 ohms, 4 puts out 8, etc.

Right, so when i take the inners two 6l6 tunes and one rectifier tube, the outputs "labelled" 4ohm, 8ohm, 16ohm "change" ? sounds a little dodge. This is a dual rec btw.

 

[JeffTD]

Yes. When you change the wattage, the output impedance also changes, unless you have different transformer's for each wattage .

 

[Familia><Publica]

why label each output with their specific ohmage if they can change ? doesnt make much sense .

 

[JeffTD]

Because most people don't run their amps at half power by pulling powertubes out.

 

[Familia><Publica]

Its suggested in the mesa user manual, i believe. Not sure where you get the idea that " most people " don't run them at half power.

 

[Familia><Publica]

im totally fucking confused now... and worried. I've been running a single cable out of one of the 8ohm outputs into one of the marshall 1960 inputs. Now... as there are two inputs one is labelled " 4ohm/8ohm " and the other is labelled " 16ohm/8ohm " and the mono/stereo switch of course. I've always assumed the mono switch gives the inputs 8ohms each and the stereo switch give the inputs 4ohm and the other 16ohm... So... Its been running out the mesa at 8ohms and into the left input switched to mono. Is THIS ok ? * cries * i hate impedance, ohmage, ive never understood it.

Edit: Have i been running the 8ohm output of the mesa into the 4ohm left input of marshall ? is that ok ??? ahhhhh, fuck.

Edit: Yup, looks like ive been feeding the 8ohm ouput of the mesa into the 4ohm mono/left input of the 1960. Guess i've fucked my amp then.

 

[JeffTD]

How many people do you know with Recto's run them at half power? And how many at full power?

You haven't fucked up your amps, Mesa's can go for awhile without being fucked up on impedance mismatches, they're tanks.

But, I'd switch it to the proper impedance ASAP.

 

[Familia><Publica]

Thing is, i dont know what ohmage is what on my marshall cabinet, what with the mono/stereo switch. Both inputs are labelled with 2 different ohmages ( left input 4ohm/8ohm right input 16ohm/8ohm. Dont even know what ohm output from the mesa i should feed the cabinet anymore....

 

[EtherForBreakfast]

DSS -

I am running 2 x 6L6, one in each outer most slot. I'm running into my Mesa 1x12 w/ 8ohm V30.

Are you saying NOT to use the 8ohm output of the head, but to use 4ohm instead?! I have *never* heard this before and am wondering where you read this? Not that I am doubting you at all, but I'd like to know a bit more about this.

 

[iekobrid]

Thing is, i dont know what ohmage is what on my marshall cabinet, what with the mono/stereo switch. Both inputs are labelled with 2 different ohmages ( left input 4ohm/8ohm right input 16ohm/8ohm.

Seems to me that since running the cab in stereo involves two cables from (presumably) the same amp, that the stereo setting switches the inputs to a matched pair of 8 & 8. Then the mono setting switches them to an umatched pair of 4 & 16, the expectation being that you'd only be using one or the other.

 

[JeffTD]

DSS -

I am running 2 x 6L6, one in each outer most slot. I'm running into my Mesa 1x12 w/ 8ohm V30.

Are you saying NOT to use the 8ohm output of the head, but to use 4ohm instead?! I have *never* heard this before and am wondering where you read this? Not that I am doubting you at all, but I'd like to know a bit more about this.

That's exactly what I'm saying. It was discussed on the Mesa forum a bit back, and the guys at Peavey told me the same thing with my old XXX and old 5150, as well as the current 5150 I have. Jerry Pinelli at FJA mods also told me this, but I'll dig up that thread at the Boogie forum real quick.

 

[JeffTD]

This site links to a page that used to be on Mesa's page that talked about it:
http://www.amptone.com/pullingtubes.htm

It has a letter from a guy at Boogie confirming what is said about pulling the power tubes and halfing impedance.

also:


So it's safe to pull two of my four output tubes?

Yes, but make sure you pull one from each side of the output transformer. Otherwise you will just have a mess. Since this changes the output impedance, you'll need to adjust either your output impedance selector or your speaker load. Here's the deal on that:

When you have 4 tubes in a push/pull amp, that's two tubes in parallel per alternation of the sine wave. When you have 2 tubes whose plates are in parallel, the plate impedance (which is what the output transformer "sees") is halved compared to a single tube per alternation. (Just like speakers, when you have 2 8-ohm speakers in parallel, the total load is 4 ohms.)

If you don't have an impedance selector on your amp, you should adjust your load such that if you're running 4 ohms with 4 tubes, you should be running into 8 ohms with 2 tubes. The actual load under 50W conditions is twice that specified by the normal 100W output tranny.

If you don't change your speaker impedance, you need to adjust the head's impedance such that the speaker load is 2X what the 100W load would be. In the case of an 8-ohm cabinet, you need to select a 4-ohm output impedance on the amp. (8 ohms is twice what the amp thinks it should be running.)

From: http://www.mindspring.com/~atlantatubeamp/id15.html/

In any case, if you're still weary, grab a multimeter and measure the DC resistance comming out the amp (round to the nearest one, often times 8 ohms will read +/- 1-2 ohms).

 

[Splat88]

When I received my triple recto 3 years ago through UPS, the rectifier tubes and 2 6L6s were busted up too. They also dropped a box of Celestion V30s I shipped to a guy. At least they payed for those because the UPS guy dropped it right in front of the recipient. It was great.

 

[andrea:::shank]

general practical rules:

1x4 ohm output goes to 1x4ohm input

1x8 ohm out goes to 1x8 in

1x16 goes to 1x16

2x4 ohm outputs go to 2x8ohm inputs

2x8 go to 2x16

some amps (engl, mesa...) have separate outs for different impedance and clearly indicate what output must be used for different ohm values

marshall cabs have:
2x8 ohm ins (in stereo mode)
OR, with the flip of the switch
1x4 ohm in (in mono mode using ONLY the left input)
OR
1x16 ohm in (in mono mode using ONLY the right input)

NEVER use both ins when the cab is set to MONO
NEVER mismatch impedances when dealing with tube amps
the worst thing of all is to connect the amp to a cab whose impedance is lesser than the amp's... oh, no, the worst is to turn on the amp without connecting it to any cab!

note that if you use only one input when the cab is set in STEREO, YOU ARE USING HALF OF THE CAB and the ohm value of your amp's output MUST BE THE SAME AS THE CAB'S IN (8 ohm for marshall cabs)!

for example, since my band's other guitarist still doesn't have a cab of his own, we often practice using my vht 4x12 cab set to stereo, and each of our amps is connected to one of the ins of the cab (8 ohms each in stereo mode) using the amps' 1x8 ohm outs.

 

[Familia><Publica]

Well, ive been running the marshall cab in mono, using the 8ohm output of the mesa into the left input of the cab, which youre saying is 4ohm. I'm getting quite stressed now. Shall i use the 4ohm ouput going into the 4ohm input? or the 8ohm output going into the 16ohm input? maybe both are ok? maybe its too late.