forte cab questions (2x12 stereo) | Warehouse Guitar Speakers

forte cab questions (2x12 stereo)

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patrick.j.hinton
01/30/2019 6:13pm

so i am looking to get this cab to run a bassman and a vox through panned stereo. a couple questions as this is an odd cab as it is.
i am planning to run the bassman into an et90 and the vox into a retro 30.
https://avatarspeakers.com/shop/guitar/3d-212-horizontal-forte-replica/

is putting two different speakers in this enclosure a poor idea? (will i have problems with phasing and the two amps/speakers fighting over frequencies)
should i purchase an et65 to put in here instead of the et90? (et90 is currently crammed in a blues jr 3, which probably is too small for that speaker)
would i be better off getting the avatar g212 vintage that you have recommended before (which is also about $100 cheaper?)
the only reason i considered this odd looking cab in the first place is because it seems that *if* the design works the way it seems it would, i might get some more stereo separation out of a single cab than just a regular closed back or open back.
it is worth noting that i understand that if i am after separation i will need two separate cabs, however i have been running this rig out of two 1x12 cabs and more often than not i end up setting it up like a micro stack, the reason i am replacing the cabs i currently have is because i slapped them together quickly and poorly years ago, and now those boxes rattle and shake and make crazy weird overtones and i need to see what this amp really sounds like through a proper cabinet.

here is the amp just for refrence (lets be honest, its eye candy!)
https://photos.app.goo.gl/JfWichtS28mPEuwp8

Narcoleptigon_47048
01/30/2019 11:49pm

AFAIK, running separate amps to each speaker means the response of each speaker will be less colored by the other, but internal reflections will have some effect. I wouldn't worry about that. Considering the cab design and narrow dispersion of 12" speakers like that, I can't imagine the high end of either will come out of the other side vent. The ~4kHz+ range of each should be isolated from each side, and the inverted ~1ms delayed side vent wave shouldn't interfere with the same freq range front waves of each speaker. It looks like it is designed specifically so the 4kHz+ range of each speaker should disperse pretty wide without interference other than right in the middle of the speakers, starting from ~4' out. Below that range there will be mixing, but that's shouldn't be an issue. I'd say go for it. I like your speaker choices. If you prefer to crank the Presence on the Bassman, you might want the ET65. I think Vox are darker amps when cranked. Someone with experience comparing the relative brightness of the two amps might know more, but you can always use more Tone Cut on the Vox at a given volume if it's too bright through the Retro.

Maybe make a note on the back of each speaker connected to each input with the impedance value and RMS power ratings.

patrick.j.hinton
01/31/2019 5:33am

thanks so much for the knowledgeable response, i may end up grabbing an et65 as you said, the amp has a switchable speaker out on each side (4,8,16 ohm)
yes i am still messing with the eq on that vox channel as it tends to be bright at low volume and darker when it breaks up, that ef806 tube sound best driven hard by a boost/drive pedal. i plan on running one of those multi jack panels that are labeled for stereo 8 and mono 4,16 ohms. the retro and et90 i own are both 8 ohm loads. thanks again for all your help!!!

Narcoleptigon_47048
01/31/2019 8:45pm

Sure thing. I assume the Bassman isn't 100W? You could also swap in your ET90 if you prefer it. A Klone Centaur is apparently the de facto standard drive pedal for a Vox ACxx, or you might prefer a Treble Booster type for a brighter sound. I wouldn't go for originals because they are way overpriced. There are plenty of clones that sound virtually identical. The Centaur is a very interesting design.

patrick.j.hinton
02/01/2019 5:05am

I have a Klone on my board, along with a timmy as well. right now I am running both power sections with kt66 output tubes, the amp is self biased so if i want i could throw el34 in the Vox circuit and 6l6 in the bassman side. with the kt66 I am seeing 30 watts per side. The amp is an sts88 from frenzel.
I might be wrong but I think the output tubes effect output wattage, so I think with kt88 I would see closer to 40 watts.

Narcoleptigon_47048
02/02/2019 8:23am

Yeah, I was a bit confused about the amp situation. Cathode-biasing rounds/cleans-up the attack. Might be nice to throw something different in one side. Bassman initially ran 5881 AFAIK, but it might make more sense to just leave one KT66 pair and run something with less bass emphasis in the "Vox" side. EL34 might be worth a try -- the smooth upper-mids might be a good idea with the bright Retro 30, and a dynamic clean sound mixed with a more dirty/compressed sound is a good bet. The KT66 might not dominate the bass and treble attack punch mixed with the El34. You might need to try KT88 if that's the case. If you don't know what to try for EL34, I'd start with the JJ EL34. They are a well-liked "neutral" EL34. The JJ KT88 are also very good. I really don't think NOS tubes are worth it, but sometimes you can find a good deal.

patrick.j.hinton
02/02/2019 10:53am

ok, trying to follow you here, i understand that EL34 is your reccomendation for the vox side, are you also saying i may want to try KT88 for the bassman side? or KT88 in place of el34 on the vox side. i agree that the retro and the KT66 make for a very bright and at times harsh amp. ill add those two pairs of tubes to my list. I wonder if I should try a 6L6GC from JJ in the vox side as well, Badcat made an amp called a Judah a while back that used an EF86 for a preamp and 6L6 in the poweramp, that is why i am intrigued.

Narcoleptigon_47048
02/03/2019 8:40am

Yes, I'm saying to try the JJ KT88 for the Bassman-ET65/90 side if the KT66 isn't loud enough mixed with EL34 in the Vox-Retro 30 side. If you are concerned that KT88 won't give that sweet Bassman-like midrange sound, try a pair of Tung Sol 7581A. They are a very full/balanced/clean/detailed 35W tube that breaks up smoothly like a 5881 -- very highly reviewed by those that have tried them, and make more sense for a Bassman sound if the KT66 don't have the power and punch. The JJ 6L6GC is clean hard and bassy. The spectral balance is virtually the same as the JJ KT88, but the high end might be "harder" than your KT66 (depending on the KT66 brand you have). The JJ KT66 is like a weak/flat sounding KT88 -- not their best effort. The Shuguang KT66 or the smoother Gold Lion are better. If you want a fat 6L6GC sound in the Vox side, but with tighter bass and the smooth EL34 midrange, maybe try the JJ 6CA7 -- probably the most reliable tube power tube JJ makes. The JJ EL34II are fat like 6L6GC, but "softer" than the 6CA7 and with the stronger 3rd harmonics that pentodes have -- sweet sounding tube, but not as clear as the 6CA7. Technically, might be more Voxy though. Since the attack clarity would come from the Bassman side, they might be the best option. The sweet high end should be nice with the Retro 30. The other option is 5881 in the Vox side -- aggressive midrange and more-compressed/less-bassy than 6L6GC or 6CA7, but tight and gets creamy when driven. I'd think EL34 would be more Voxy though. Some other EL34 brand might be better, but I don't know off hand. My impression is the Mullard RI and other recent Russian EL34 tubes are more mushy than the JJ. That's why I'd try the JJ EL34 or EL34II first. Being an ultra-linear design, I'm not sure how much tube overdrive the amp generates. I guess it depends on the transformer tap values:
https://www.ampbooks.com/mobile/amp-technology/ultralinear/

patrick.j.hinton
02/04/2019 9:10am

Thanks again for all of your help! I really appreciate you taking the time to post all this knowledge! I will certainly be picking up those recommendations over the next couple months, the cab will come by soon enough and I'll let you know how it all goes!

Narcoleptigon_47048
02/05/2019 2:45am

No problem. I find doing research interesting. I'll just mention a few more things about the tubes I suggested. Power tubes don't make all that much difference until they are driven. Even then it's not that much, but it's worth finding something you really like if it's not a big expense.

Some the TGP forums say the JJ EL34II is "brighter" than the 6CA7, and that it's the "darkest" of the JJ power tubes. Opinions are divided, but they may worth a try at some point. Either tube will sound softer and more-compressed at the low plate voltage of your amp. More mushy tubes might then be too mushy for your taste. I think the 6CA7 is the less mushy, and perhaps less resonant, of the two. They sound really huge in old Plexis without getting muddy like 6L6GC.

The KT66 you have may be close enough to an EL84 sound anyway. You might just stick with those, and maybe just try the Tung Sol 7581A in the other side if the speakers don't quite make the difference you want. I'd get any JJ tubes in matched sets from either Eurotubes or TheTubeStore to maximize odds of getting good ones (any tube from any brand can fail even after testing). TheTubeStore also has the TS 7581A.

patrick.j.hinton
02/07/2019 12:30pm

Those two tubes aren't listed on the manual (7581 and 6ca7) I'll have to check with the manufacturer to make sure they will be comparable. I dont want to harm the circuit.

Narcoleptigon_47048
02/13/2019 4:33pm

The Tung Sol 7581 is just a repackaged 6L6GC. The 7581A I recommend is a better tube, and will work with virtually any amp that takes 6L6GC. You may get ~35W from a pair instead of 30W. The JJ 6CA7 is a direct EL34 replacement with a 500V G2 limit (vs 450V for most EL34). Maybe just try the speakers first anyway.

Update: I looked at the ST88 amp on the Frenzel site, and it lists 30W for KT88 tubes. The JJ KT88 are rated as 600W/42W tubes, so the plate voltage of the amp must be ~250V? I'd guess two 550V/25W KT66 would then yield ~20W in cathode-biased push pull at 250V. EL34 should then do ~22W. A 7581A pair should do ~30W, and keep up better with the KT66/Vox side with the "edge" (No NF) switch engaged. I'm really thinking that's the first tube set to try changing. I'll try to otherwise distract myself from this in future. LOL.

patrick.j.hinton
02/26/2019 11:36am

Ok so run 7581a on bassman and run kt66 still on vox?or switch to el34, what set of 34's did you reccomend? The 34's will get 22watts vs kt66s at 20 watts?
The 7581a will push how many watts?(duh, u just said ~30) In general the ac preamp isn't as loud as the bassman. So if the ac output is higher that's ok. Sorry I didnt respond for 2 weeks!

Narcoleptigon_47048
02/26/2019 6:04pm

I'd first just try the 7581A in the Bassman side for ~30W. Can't say which EL34 to choose if you aren't happy with the KT66 in the Vox side. I just tried to describe how some EL34 types would sound. Yes, a real KT66 pair will put out ~20W because it is a 550V/25W tube vs the EL34 which are 500V/25W tubes. They also take more gain to distort, so they won't generally sound as loud unless cranked hard. They also don't compress as much as EL34, so they have stronger fundamental note response. In that way, I feel they are closer sounding to EL84 than EL34. Which KT66 brand do you have anyway?

Vox AC amps don't use any neg feedback, so you should engage the "Edge" pull knob on that side for a more Voxy sound. I imagine the volume between the channels will even out when the Gain and Master knobs are up, so I'd think you'd want the extra wattage on the Bassman side for the cleaner attack sound to come though.

Incidentally, I noticed the Harley Benton 2x12" cab is inexpensive and very well-reviewed. You might consider one of those, then just remove the handles and screw/glue in ~45d angle reflecting boards inside the back to get a wide stereo effect. Probably easy to do if you are comfortable building things. You'd save some serious cash.

patrick.j.hinton
02/28/2019 5:34pm

JJ KT66's
I will likely keep the 66s in the vox side.
The amp in general sounds way better with edge engaged (no negative feedback,) I currently have et90 and ret30 in 8 ohm. I am gonna go out on a limb and say et90 will be right at home at the end of that bassman circuit. Is the ret30 still a good choice for the vox side or should I shoot for something else? Blackhawk alnico 50???

Narcoleptigon_47048
03/01/2019 6:46am

Makes sense that the amp “needs” the Edge engaged with the JJ KT66 -- they are reportedly rather flat/sterile sounding. It must sound more lively without NF damping them down. JJ tubes are also kinda “hard” sounding. I think it’s a tight vacuum. The GL KT66 are smoother if you feel like spending the money. Otherwise, the JJ EL34II are a soft sounding tube for ~⅓ the price. Possibly the only one without a very tight vacuum. Much more harmonics than the JJ KT66 -- fat and somewhat bright, but not harsh. Maybe try a pair of those. It may be boomy with the Edge on. Turning the bass down should solve that. I'm also curious about the preamp tubes. Stacking different types brands can alter the character a lot. Not sure if the amp has a phase inverter stage, or what type it is. I'd at least put a nice long plate tube in that stage if you have a choice. Specifically what are the preamp tubes?

Yeah, I thought the ET90 might be good for a Bassman sound. I’d still try those 7581A driving it at some point. Probably smoother than the JJ KT66.

I could be mistaken, but I think the Retro 30 is a ceramic BH 50. May not be much difference -- less bass and slightly sweeter high end? My guess is the EL34II or GL KT66 may soften the high end enough with the Retro. You’d have to experiment.

patrick.j.hinton
03/02/2019 7:30am

v4 (L-preamp/bassman) 12ax7, v3 (L-driver) 12ax7, v2 (R-driver) 12ax7, v1 (R-preamp/vox) ef806
v5 (l-phase/inv drive) 12ax7, v6 (r-phase/inv drive) 12ax7, v7-v8 (l-output), v9-v10 (r-output), v11 (rectifier) gz34 all this is jj except rectifier, it burnt out and was replaced with gt

Narcoleptigon_47048
03/02/2019 12:21pm

I actually meant which brand and specific type. I assume the L & R "output" are power tubes? Don't Bassman normally have a 12AT7 for the phase-inv? I wouldn't change that unless the socket is biased for it -- may sound too brittle. In any case, the standard JJ ECC83S is considered a fairly dark tube. Either way, stacking a few tube plate types should fill out, open and sweeten the tone, and add some subtle complexity via different plate resonance, rather than the same resonance stacked. Here's what I'd do:

-Try a JJ ECC83MG (Medium Gain/plate-size) in V2 and V3 and/or V4. It's a better (sweeter & more open) sounding tube. The gain difference is only ~5% less than the standard ECC83S.
-Try a JJ ECC803S (long plate) in V5 & V6. You could instead try a Sovtek 12AX7LPS in either slot. It's a more mushy and harmonicy tube some players prefer. For that money, you might look for a long plate IE 12AX7 if you can find one cheap. Do not use the long plate "spiral filament" tubes in cathode follower slots. They can't reliably take the cathode voltage.

Those four tubes should total $60~75. Not that much difference, but you may notice some subtitles like cleaner bass and better high end detail. It certainly won't make as much difference as a speaker change, but more a matter of fine-tuning the response character. You could try recording b4 installing them, and again after to see if you can hear it.

patrick.j.hinton
03/21/2019 9:30pm

ok so I am getting ready to pull the trigger on the cabinet now, i am honestly having second thoughts on the forte cab. i am wondering if i should go with a larger open back cab instead. obviously this rises the same concerns from the OP wondering if ill have freq cancelling eachother out. but reading all the posts and reviews here, there are tons and tons of posts regarding both the avatar g212 vintage ran 1/3 open back and also a lot of talk about how larger cabinet volume is generally better. the g212 has a volume of 8,820 cu in. the forte cab is 7,511 cu in. its got a closed back but the open sides will still project, i am just imagining maybe not as much? is there any telling how much this size difference will effect overall volume? with the amp running 20 watts i would imagine that cabinet choice could be the difference between this amp having enough oomph to keep up in outdoor gigs and not. also, if the forte cab is going to be significantly better at making the amp project a stereo image then ill take the lower volume. the gigs i currently play i am always mic'd anyway. thanks for all your input!

Narcoleptigon_47048
03/22/2019 4:47am

AFAIK, cab size/volume does affect the bass response via air compression and where the cab resonance freq is. Both cabs are essentially open back in this case, so compression isn’t really a factor. The Fs (Free Air Resonance) of each speaker cone should be the dominant factor in bass response, around which points it will be louder, Considering the relative size of the openings, both cabs may be tuned about the same. So the difference in internal volume might end up causing something like a 0.5dB or less difference in bass response above the cab resonance -- which would be in the mid-bass region. My guess is that difference will be insignificant compared to the bass response traits of the speakers.

Since the Forte cab projects the high end from each cone back forward, effectively dispersing it where you’ll hear it, it should have a better stereo effect -- probably over 2x wider above ~2kHz (where stereo imaging really starts to matter). The cab would still need to be tilted back or placed up near ear-level to hear ~4kHz+.