Do I need to lower speaker impedance when changing from 6v6 to 6L6's?

[Normybaby]

My friend is a jazz guitarist and he has a 74 Deluxe reverb that he wants me to MOD so he can have more clean headroom. He printed out some info on-line that suggests installing 6L6’s, solid state plug-in Rectifier and a beefier speaker. The amp is all original so it will need new filter caps and I was thinking maybe to double the value on the main and screen grid filter caps (maybe to 47mfds).
My question is, should I get a 4 ohm or 8 ohm speaker. 4 ohms would produce a reflective primary impedance to match the 6L6 but would that produce too much demand on the power transformer..
Nothing was mentioned in the MOD specs about changing the speaker impedance

Thanks
Norm

[Jazz P Bass]

The Deluxe Reverb is not known for loud, clean.
I doubt that the 6L6's are going to get you there.
My take is that there is not near enough B+ voltage to get the amp into the "Twin" clean.

[MWJB]

A deluxe reverb with 6L6s, a SS rectifier (even a GZ34 - '74 will have a 5U4 as stock) & an efficient speaker is a pretty loud amp, even without adjusting speaker impedance. I'd go to 100uf total on the main filters & 40-50uf at the screens, rewire the mains using 2x220uf in series, each cap bypassed with a 220K 2W resistor (see Super Reverb for the general idea). Your choices of 4ohm speaker are going to be somewhat limited, not a problem if you know what you want, but I'd be more inclined to add another 12" ext cab at 8ohms...but you don't have to, the higher primary Z will limit current through the primary at a given output.

Bias to around 30mA per tube.

No it won't give you the whump of a Twin, with the Twin's bigger transformers, but B+ may be comparable with many Twins (130vdc variance in models) and it won't give much away to many amps of 40-45W.

[kg]

clean headroom is all about the power supply. switching to ss rec will help, bigger filter caps may get you a LITTLE more punch, but mostly you need that b+, as jp bass said.

[kg]

and +1 on adding more speakers. that's the easiest way to get bigger sound.

[Earl Norton]

efficient speaker is the way to go. EVM or JBL d120f will get it to crank some DB's without other modifications. 18 watts is a loud amp with the right speaker.

[ballynally]

efficient speaker is the way to go. EVM or JBL d120f will get it to crank some DB's without other modifications. 18 watts is a loud amp with the right speaker.

All depends on your drummer, i.e, the Deluxe reverb is around 20 watt and is exactly the way it's supposed to be. Not all rock drummers are loud drummers as not all jazz drummers are soft drummers. I would caution you trying to mod the Deluxe extensively, including beefing it up to try and get to 40 watt Bandmaster or even Twin mode. I would go and get a separate amp head. Don;'t know if you're wedded to tubes, because a solid state amp is a good option if you want to stay clean.You can get a good small SS amp head around 100 Watts that doesn't weigh a ton and then get a seperate speaker cabinet.For jazz i think an EV is good as it gives you an uncoloured clear sound, but they are very heavy, and not needed for a 20 watt amp like the Deluxe. I would recommend the Eminence Cannabis Rex, a 50 watt hempcone speaker. Very balanced throughout the freq. spectrum. It's simply great for the Deluxe reverb. The jbl s have those piercing highs and tight lows. Great if you need the speaker cranked up, but i do prefer the Eminence and the EV for their warmth

[kkillebrew]

You can use the 6L6's and rebias but you won't get any more volume because of power supply limitations. Also, the Deluxe is likely to have a 2 amp or so 6v filament winding. If so you are risking the power transformer by using 6L6's. I built a Tweed Tremolux with a 3 amp filament winding just so I could do this, but I only tried it once because there was little tonal difference and no output increase.

[MWJB]

You do get more volume, with 6L6s and a more efficient speaker, the deluxe is perfectly able to tolerate 6L6, it has a 3.5A heater winding typically...this would appear to be a conservative rating...besides, removal of the vibrato tube (V5) & V1 (whilst rebiasing V2 triode b cathode with a 1.5K resistor) will restore 0.6A of the additional 0.9A that 2x6L6 will need. Final B+ will depend on rectifier (you can't usually use SS with NOS 6V6s, but you can with 5881/6L6), brand of tubes and how they are biased, you can see 430-440vdc at the plates...y'know about the same as on a "40w" Vibrolux, or a Blues DeLuxe ;-). I have upgraded several Deluxe Reverbs to 5881/6L6 and efficient speakers...the next thing I hear from these owners is "how do you get them to break up at lower volume, it's too loud for half my gigs?" & "why is my 25W (it isn't 25W anymore) amp louder than my 35W/40W amps?".

If you like the size & weight of the Deluxe, the retube route is a pretty cost effective & back friendly (as long as you don't fit a big cast frame EV in there) route to improved volume & dynamic response...will it eat Super Reverbs & Twins for breakfast? No...2x10" Vibroverbs, Tremoluxes & Vibroluxes? Yes, most of the time.

[Chuck H]

Just a note... The article probably doesn't mention the speaker/OT primary mismatch because the DR OT is probably already a good match for 6L6 tubes when Vp is 430 (ish). 6.6k is a kind of generic value for 6L6's around that Vp. Should work fine. Stick with an 8ohm speaker. Eminence makes a few really efficient speakers and they all have that classic Eminence boxy rolled off treble tone which is usually good for jazz. While your at the mods you might try a 5751 tube in the first preamp socket for the channel he uses. It won't actually give more headroom but it will make so the amps max clean volume is a little higher on the volume knob setting. He will most likely percieve this to mean the amp is louder now and like it, whether it's perception or reality it'll make him happy.

[Normybaby]

Thanks guys. I am suggesting to use a Jensen neo 12". I have a 12" in a 30 watt custom amp I built (based on a high output Princeton reverb) and it sounds awesome. I also have a 15" Jensen neo in a separate cab that sounds incredible....that's why I'm recommending the neo to my friend...There is a Utah in there now that sounds good at low levels but tends to break up at high volume. I will suggest that he go with the 8 ohm speaker, SS rect. and I will install the larger filter caps.

I appreciate the suggestions and I feel a lot better that you guys have had firsthand experience and knowledge on the subject. Thanks so very much for your help
Norm

[Chuck H]

The Jensen neo 12 has an SPL of 98.8dB... Pretty average. Probably 1dB higher SPL than the Utah so you won't hear much difference in volume. Now something like the Eminence Cannabis Rex, Man o War or Wizard will be notably louder than that Jensen neo. Louder = more clean headroom. If your guy is after clean headroom and wants the amp louder you shouldn't overlook this important detail or the results may be lack lustre. Using a speaker with 3dB more SPL than the stock speaker is like doubling your watts in loudness. As an example, the Cannabis Rex is probably about 4.5dB more sensitive than the Utah. A Wizard would be 5.5dB more sensitive. It'll be like the amp took steroids. With the mods and a Wizard the amp would be about twice as loud as it is now.

[JoeM]

I have a DRRI, and even stock, with an Eminence Swamp Thang speaker is amazingly loud.

[Chuck H]

Swamp Thang is SPL 102dB like the C Rex. Probably too agressive for jazz but it supports the point. Thank you.

[JoeM]

Swamp Thang is SPL 102dB like the C Rex. Probably too agressive for jazz but it supports the point. Thank you.

Yes, that's my point exactly. An efficient speaker is the single most important change if you want the amp to play louder.