NAD Mark IIb

[gpuma]

I found a mark IIb with an interesting story locally and I yield to the Force of AAS.
I also am in the middle of a move from Chicago, IL to San Juan, PR and accumulating more gear is not exactly the smartest action so I justified the purchase by (very regrettably) selling my 5:25 Express Combo (the first series with the 10" speaker).

Apparently this MkIIb started its life in 1981 (sold in 1982) as a combo and it was converted in 2002 to a head + 2 1x12 cabs each featuring an Altec 417. The amp came with pages over pages of original papework. One sheet seems hand signed by the man himself RS and his wife. It seems in really good conditions. It also features Graphic EQ, Simulclass and Reverb.
It currently has 2 EL34 and 2 6L6. I have a set of new Mesa 6L6 that I might put in though.

The cab is a widebody 1x12 cab that is more modern than the amp. I am not exactly sure how Petaluma had still available some Altec 417 in 2002. Weren't they long gone by then?
Also the speaker is labeled as a 418 which is the 15" brother of the 417 but it is definitely a 12" speaker so I am not exactly sure of what it is. Sounds pretty awesome to my ear and that's all that matters.
A couple of pics...

 

[dodger916]

Nice amp! The speaker was not necessarily installed by Mesa.

 

[gpuma]

Is there any caution I need to take in using EL34 instead of 6L6, other than matching the pair?
In the Mark V there is a switch for adjusting the bias

 

[bgh]

I have never heard of using EL-34s for all 4 power tubes in an older Mark. I know you can go with 4 6L6s, and (with some restrictions) you can use 4 6v6s in a Mark IV. But I don't think you can use 4 EL34s.

Hope this helps.

 

[gpuma]

Thank you.
What about EL34 only for 2 tubes, like the configuration I found the amp with?

 

[bgh]

That is a good question.

I went to the Eurotubes website and found the following (I added the highlighting):

The Mark II series amps from the original Mark II thru the Mark II C plus vary widely. If we were to list all of the variations and possibilities there would be in excess of 300 kits! So our decision was to list a “Custom Kit” page for these amps. About the only thing near constant with the Mark II series amps is they all use a long tail Phase Inverter circuit and the PI tube is almost always located closest to the power tubes. The Mark IIB amps come in 60 and 100 watt versions, with verb and without verb, with and without EQ. Some of them with verb use a 12AX7 (ECC83) and some use a 12AT7 (ECC81) for the verb. This is usually noted on the chassis written in black felt pen. The Mark IIC and C Plus amps came in both 60 and 100 watt and some 100 watters are also Simulclass allowing the use of a pair of EL34 type tubes in the middle two power tube sockets. So to order a kit for your specific Mark II amp you need to know what tubes it uses! If you don’t know then take a look under the hood to make sure you’re ordering the right tubes. If your amp uses five preamp tubes then check your V4 preamp tube to see if it’s a 12AX7 or a 12AT7. Do not use any of the power tube combinations with 6L6GC’s and EL34 type tubes unless your amp is a Simulclass series amp. *** If you are unsure about selecting the right tubes just give us a call!

On the pictures you have, I did not see a Simulclass switch.

Perhaps a call to Mesa for double-verification would be in order. (I have called multiple times, They are extremely helpful!)

Hope this helps.

 

[gpuma]

Very helpful indeed. Thank you. My amp is simulclass. The switch is right of the heat sink and I didn't take it in the pic.
Thanks again!

 

[dodger916]

That is a good question.

I went to the Eurotubes website and found the following (I added the highlighting):

The Mark IIB amps come in 60 and 100 watt versions, with verb and without verb, with and without EQ. Some of them with verb use a 12AX7 (ECC83) and some use a 12AT7 (ECC81) for the verb. This is usually noted on the chassis written in black felt pen. The Mark IIC and C Plus amps came in both 60 and 100 watt and some 100 watters are also Simulclass allowing the use of a pair of EL34 type tubes in the middle two power tube sockets.

Inaccuracies here:
1) I thought the IIb was the first simul-class amp.
2) Simul Mark IIs are 75 watts, not 100
3) EL34 in the OUTER SOCKETS, not middle two sockets. I would have thought Eurotubes would be accurate on this....

 

[gpuma]

Thanks a lot for clarifying Dodger!
My amp is Simulclass indeed

 

[bgh]

That is a good question.

I went to the Eurotubes website and found the following (I added the highlighting):

The Mark IIB amps come in 60 and 100 watt versions, with verb and without verb, with and without EQ. Some of them with verb use a 12AX7 (ECC83) and some use a 12AT7 (ECC81) for the verb. This is usually noted on the chassis written in black felt pen. The Mark IIC and C Plus amps came in both 60 and 100 watt and some 100 watters are also Simulclass allowing the use of a pair of EL34 type tubes in the middle two power tube sockets.

Inaccuracies here:
1) I thought the IIb was the first simul-class amp.
2) Simul Mark IIs are 75 watts, not 100
3) EL34 in the OUTER SOCKETS, not middle two sockets. I would have thought Eurotubes would be accurate on this....

All I did was a copy-and-paste from their web site.

To be honest, all I paid attention to was their comment that the only time you could safely mix EL34s and 6L6s was it the amp was simulclass. I didn't even catch their comment about the middle sockets. I run EL34s in the outer sockets of my Mark IV.

The OP indicated his amp did in fact have a simulclass switch, so he should be good to go.

My apologies. I will watch out in the future.

 

[gpuma]

Thank you sir, no apologies needed.
I have to thank you for taking the time to reply!

 

[gpuma]

I have another question.
What exactly is this fx loop mod? Why would I need it?

 

[Tuna141]

I think the Eurotube site in incorrect regarding the EL-34 tube placement. I'm pretty sure that the EL34's can only be used on the outside pairs in a Simul-class amp. That is, unless the IIB amps were different than the other Marks.

 

[dodger916]

My apologies. I will watch out in the future.

No worries; sorry if it came across as a jab at you. I was criticizing Eurotubes, very knowledgeable tube dealers who really know their stuff and who have helped me several times in the past. It just surprises me that such knowledgeable people would publish such inaccuracies, especially when tube placement is concerned. I will drop them a line to correct their website, so you actually did a good thing by (inadvertently) pointing out their errors!

 

[gpuma]

Finally I was able to spend few minutes with the amp.
I love it so far. It is surprisingly noisy, a lot of humming noise.
I read few threads about it and it seems like it is a common problem with these vintage boogies.

Does anyone know of a good tech in the Chicago area that could take care of the issue?

 

[xdg999]

Chicago Fret Works has a really good amp tech.

 

[gpuma]

Thank you, I know them; they are few blocks from my home. They do very good work but their rate is very high and their customer service is pathetic. After being robbed few times I'd rather go somewhere else.

 

[xdg999]

Sorry to hear that.

 

[gpuma]

To be honest I had problems only with the lutier but I just decided to bring my business somewhere else though. Thank you for your answer anyway

 

[DC3 Gridlock]

I own a 1982 Mark IIB Simul-Class combo. Mine was made in April and has Mark IIC knobs, blue tolex, and a silver grill.

I changed my amp over from the two EL34 and two 6L6 combination to a new quad set of Mesa 6L6's.

To me an improvement in tone, especially on the clean channel.