66 Super Reverb 8 ohm Single Altec Lansing 12

[jjnet]

I've owned a blackface Super Reverb for years with only about 15 hours use in that time. (My acoustics take up most of my playing hours).

When I got the Super there was a single no-name 15 inch speaker which I've replaced with a 1973 Altec Lansing 12 incher. I put a double 12 baffle in but currently have my second Altec 12 out on loan to a friend.

What are the risks to using it with an 8 ohm load? I have no idea how long the 8 ohm 15 was in there, but I'd bet it wasn't used hard with that speaker.

I run the volume 6 to 8 with the Altec 12. The amp's had no maintenance of any kind in 35 years. I've never changed a tube and it's possible the tubes are all or mostly original. I'm assuming it needs caps and probably some resistors. What kind of cost am I looking at for that work? And what improvements should I expect?

The only obvious issue is a scratchy reverb pot. I have no idea if the trem works as I have no footswitch with it. I definitely don't want to risk damage from a wrong 8 ohm load now that I'm using it again. Thanks for giving me the benefit of all the accumulated wisdom on the site.

[Chuck H]

If someone put a 15" speaker in it that would require some work. It's possible then that someone also changed the output transformer to match the new load (though unlikely). It would be worth checking the numbers on the transformer to see what it is. If it is a Super Reverb output transformer it's designed for a two ohm load. Running that amp on 6 or 8 is pretty much full blast with your guitars volume control up. So that would mean your possible running the amp full blast into a 400% load mismatch. It's also worth noting that at some point a higher load is more dangerous than a dead short. I can't really endorse that. It may never hurt the amp the way you use it, or it may. It's far enough off that I can't even say "Eh, it should be alright". Adding the other 12" would put you at a four ohm load (which is a 100% mismatch). This is almost always fine, as evidenced by the "ext. speaker" jack on the back of the amp. Do check the transformer.

At that amps age I would say it certainly needs new capacitors in the power supply, bias supply and preamp cathode bypass caps. Since it's had very light use your tubes may actually be fine. The scratchy pot is usually an easy fix. Old carbon comp resistors are known to drift so these should be checked. some contact cleaning, etc. How much??? Probably a couple of hundred + parts.

[MWJB]

"I run the volume 6 to 8 with the Altec 12. The amp's had no maintenance of any kind in 35 years. I've never changed a tube and it's possible the tubes are all or mostly original. I'm assuming it needs caps and probably some resistors. What kind of cost am I looking at for that work? And what improvements should I expect?"

Speaker impedance seems to be the least of your worries at the moment. A cap job will restore the detail & presence of your amp, new power tubes and a 12AT7 in V6 (PI) are a good idea, when a power tube fails it can take other parts with it. The other 12A#7 tubes? Well, it's entirely up to you which & how many you replace, assuming that you have no unusual/unwanted noise. Cap job, new power tubes & PI tube may run to a little over $250, but will ensure that your power supply is healthy for another 15-20yrs.

Use a small crocodile clip, or a shorted RCA plug to activate the tremolo.

Speaker impedance floats with frequency (impedance rises with frequency, but a higher ohm speaker will also reduce highs), I wouldn't think twice about running the Super Reverb with a 4ohm load...but 8ohms does jack up the voltages in the OT, though it also greatly reduces currents there too. As you have space for 2x12"s I'd buy another 8ohm 12" to go in there, wired in parallel with the one already fitted, for 4ohms overall. It doesn't need to be another Altec Lansing.

If you have a penchant for very expensive speakers, it may be cheaper to sub the OT for a multitap version (if you're getting the amp serviced anyway, a new OT will only run to the price of the part plus 30 mins install time)? Then you could change between 4 & 8ohms at will & safely.

[pdf64]

'new power tubes and a 12AT7 in V6 (PI) are a good idea'
Agree with everything so far apart from the above - unless there's something to indicate that the tubes are a problem, I can't see the benefit.
The tubes in there may be performing better than new production ones and have proven their reliability.
I hate it when guys insist on new tubes fitting when the old ones are fine.
Pete.

[MWJB]

Well, that will be determined at the service...it depends how much use they have had of course...usually, 35yr old amps with tubes that have had hard use, sound better with new tubes. Power tubes take the most punishment, PI is next on the list....even then, a quick tube sub will give the answer on whether they *need* to be changed.

If someone is gigging regularly, new tubes with a 6 month warranty offer a degree of peace of mind. Luckily in a SR there are often "spare" 12A#7 tubes that can be swapped about in an emergency.

My viewpoint (rightly or wrongly) is that tubes that can cause a "no go" failure, taking out screen grid resistors, or possibly 10oohm virtual CTs (rare I agree, but feasible), get replaced at a service (unless provenance on the current fitment can be provided), then the customer can experiment with tubes that simply affect tone/microphonics. If they want me to run through their first 3 or 4 options on each preamp tube in a 5 or 6 preamp tube amp for them, then that can go on at an hourly rate! ;-)

Usually people turn up late to pick up amps, so I've had a chance to identify any obvious shortfalls in advance of them auditioning the amp & they can use their own ears to make the judgement call on whatever excess they spend. It is rarely necessary to change EVERY tube in an amp. Other times a client will request exactly that.

[pdf64]

Thanks for detailing your rationale, I take you point, but I don't get how the PI is thought to have a harder time than any other pre-amp tube. In terms of plate voltage / dissipation the reverb driver V3 is surely way ahead? V6 seems to have less stressful operating conditions than the others.
And in an SR there's the rectifier to consider; in operation they are pretty stressed but again they can work forever whereas new ones are perceived to have lower inherant reliability, so I'm loath to replace a good old one just because.
Pete.

[Chuck H]

The OP said:

I've owned a blackface Super Reverb for years with only about 15 hours use in that time...

I have no idea how long the 8 ohm 15 was in there, but I'd bet it wasn't used hard with that speaker.

And I'd bet he's right. If the amp were run hard into a 400% mismatch it probably would have failed long ago. So... If the amp was used lightly AND into an 8 ohm load (which is much lower wear on the power tubes than a 2 ohm load) I think it's very possible that the power tubes are still good.

[MWJB]

NOS 5AR4 are pretty fragile, compared even to modern 5U4, which are pretty bulletproof. The Chinese 5AR4 had a bad rap, bt the Russian ones seem good...however, rectifiers are usually working or dead & have long lifespan, they usually take a fuse with them when they fail, saving damage to the rest of the circuit. I don't replace rectifiers as a matter of course.

12AT7 - The PI is an essential tube, the reverb driver is only necessary for the reverb effect, you can finish a gig without reverb but not without a PI, but I guess as long as one of them is a known good tube, you have a "get you home" fix on hand.

[pdf64]

'12AT7 - The PI is an essential tube, the reverb driver is only necessary for the reverb effect, you can finish a gig without reverb but not without a PI, but I guess as long as one of them is a known good tube, you have a "get you home" fix on hand.'
Also in a pinch, a 12AX7 can be subbed in to V6. A small change in the response of the amp but once the drummer kicks in, hard pressed to tell!
Regards power tube wear, mismatching 'up' reduces plate dissipation but increases screen grid dissipation, but it's probably not significant unless the amp is pushed.
On the subject of 'get through the gig' fixes, what spares does anyone else advise a working muso to keep with them?
A spare or 2 of each external fuse type, and a spare for each cable? I'd rather they take a spare amp, preferably Si type, rather than have spare tubes, as they invariably get damaged unless stored carefully. But one buddy insisted he needed to keep THAT amp running, so I had him get 8 matched power tubes, so he could sub a set in without rebiasing, a 12AT7 and a couple of 12AX7s. He keeps them safe in a photographers case and has even swapped the power tubes over between sets on a couple of gigs, when he thought the response was getting squashy.
Pete.

[MWJB]

Ha, ha...I often prefer the 12AX7 in V6 on a BF/SF Fender!

Spare amp is the best policy (then there are no worries about a blown tube eating a screen grid resistor) ...nothing more infuriating than someone bowing a fuse, with no spare, in the first set when you know they have 2 or 3 more stage amps at home and an empty trunk in the car!

+1 on the spare power tubes method too...if I'm retubing an amp I'll often offer the player the option of a spare set of "drop in" pre selected power tubes (if you go through a lot of one brand of tubes it makes sense to buy matched quartets, or even octets - better odds of finding good matches for a working set & a pre-matched, back up pair). Or, sometimes a new set will run ball-park with a used, but still good, old set...& the old set can be used spares for a "get you home".

[jjnet]

thanks!

I really appreciate all the time you guys took to answer my questions on my Super Reverb. It sounds like I should consider getting my extra Altec 12 back to bring the load to 4 ohms and/or look into a multi-tap output transformer. And get the caps and resistors checked/replaced as needed as well.

One other question: I just read here that JJS 6V6S power tubes with rebiasing could be used on this amp to give me the sweet breakup I love but at lower Deluxe Reverb style volume. Any thoughts on whether this is a good or risky idea?

The ultimate irony is that I lived on an original Deluxe Reberb I bought new in April 1965 for most of the years I played a lot of electric, but sold it and got the Super in the mid 70's when we all needed more power before good PA's were everywhere. But I never gigged with the Super, only with the (then) underpowered Deluxe. These days the blackface Deluxe Reverbs are worth more than the Supers and Twins we lusted after in those days because with today's PA's they're more versatile than the higher powered amps.

I would love to bring the Super down to Deluxe volume with the breakup I love still there. If the 6V6S tubes are a viable idea I'll definitely go for it.

[Chuck H]

This is JMHO but I don't think that's a good idea. With modern wall voltages your SR probably has about 480V on the plates. While the JJ tube is said to handle it I don't know for how long. The other thing is that the JJ tube will be very near it's max 14W dissapation under these conditions so your output wattage would be about 26 or 28 watts. Considering that your SR probably puts out about 43 or 45 watts now your not looking at a very big volume difference. Maybe two dB. You might do better to try a different volume reduction method like an attenuator or dropping the screen voltage and stick with 6L6 tubes. Even less efficient speakers will get you more volume reduction. An SPL reduction of 3dB would be about the same volume reduction as cutting your watts in half. Personally, I'm an attenuator guy. It allows you to do any volume at any setting in any circumstance from bedroom practice to outdoor gig. And all with the same amp. Which has the distinct advantage of knowing what settings and outboard gear you want to use with that amp anytime.

JM2C

[Bruce / Mission Amps]

Adding to Chucks reply,
You can run the Super Reverb with a pair of JJ6V6s and a NOS 5U4G or NOS 5V5GA rectifier tube. You could even try a Russian 5Y3GT.
Reset the bias voltage so the power tubes are idling at around +10-11 watts each, Oops, you do know how to do that, right?
The JJs will handle close to 15-16 watts at idle if the B+ is not too crazy high!
The softer rectifier tubes will get your B+ lower.
Now, pull the speaker lead wire off of one speaker so the output tranny is running at 2.67 ohms on it's secondary.
I think it sounds cool like this but it will still be shockingly loud!! Louder then your Deluxe Reverb was, ha ha