I finally got that cab! This amp sounds amazing now! I haven’t messed with tube changes yet as I am so thrilled with the current results. It still has plenty of low end and man everything sounds so full. The only complaint I have is that I have to run the gain on the vox channel at 3:00 to match the volume on the bassman side (with gain at 9:00)
This is due to the nature of the preamp circuits, the bassman pre just has higher output compared to the vox. I have thought about even sticking an eq,comp, or boost in the FX loop of the vox just to boost the output of that channel. Your thoughts?
I assume both master volumes are up the same? Both Edge switches set the same?
Be better to drive the EF806 harder. I assume the tone stack is configured after it. Try cranking the Middle knob way up and adjust the Bass and Treble for tonal balance. The Middle knob is what really drives the PI/amp section. Maybe you can add one 12at7 or 12au7 triode stage b4 the EF806? Might not be as hard as you’d think if the power transformer can handle it. One of the first 12ax7 triode stages in the Bassman may be unused, or you might be able to split it to form a new Vox input? Otherwise, you might just try a JJ 5751 in the first Bassman slot (V2?). That will make some difference without really altering the tone, but I think the JJ 5751 is a better sounding tube than the ecc83S anyway. The other preamp tube changes I mentioned may help too. Cheaper than a new pedal in most cases, and I think you’ll prefer the results. Those TS 7581A power tubes should be almost 2dB louder than the KT66 at the same Voltage. That would bring the level of the Vox side up. Incidentally, most seem to agree that the Shuguang KT66 are the best sounding new KT66, but see what you think with the better preamp tubes first. Inserting a SS pedal into the FX loop will defeat the V4<->PI tube impedance interaction. You may notice a slight tone/response change.
V2 is the vox side driver. V1 is the 806, you think i should use the 5751 as a driver for the vox? Or as a preamp for the bassman (v4 is bassman preamp and v3 is bassman driver.) ill try cranking Mids tonight.
Also checked the website again, as far as preamp tubes go for that amp… Tube Complement: comes standard with 6 - 12AX7, 4 - KT88, but you can substitute 12AT7’s or 12AU7’s in the preamp for different tones and overdrive sounds. (Only difference heķre of course is that mine came with a different power tube and the vox preamp is a different circuit. But I would imagine that the rule is the same, I can swap preamp tubes.
Also, I actually had the bassman set to a lower power setting so the vox could keep up easier. There is a three way power setting for 1/4, 1/2, full for both channels.
You don’t really need to use lower gain tubes If you have separate power settings for each amp. I had intended to recommend the 5751 for the Bassman driver, but I’d try an ECC83MG there if the amps have separate power settings, unless you want significantly less gain.
Yes, you can substitute a 12at7 or 12au7 in 12ax7 slots, but the baising won’t be right as is. A 12au7 might be too grainy and unbalanced sounding. A 12at7 will be cleaner and have slightly more high end. You might like one in the Bassman PI slot if you want less preamp to power amp gain and higher sparkle.
V5 & V6 are PI slots, right?
V5 and ve 6 are Phase inverter yes. I did mess with the MIDS I noticed that they do push the amp a bit harder when cranked, you can especially notice this on the bassman side of things because the amp is set at the edge of breakup anyway so it definatly gets harrier. I am starting to wonder if I actually can get the ef806 to clip or if what I am actually getting is speaker breakup when I dime the vox. That retro is what? 70 watts i think? They say that the 806 has plenty of gain and headroom, so maybe I should just crank it and run it for a while, get used to it and change more variables down the road after a bit.
AFAIK, You can’t overdrive the V1 EF806 unless you drive it with a pedal or something. It’s a high gain pentode that does not drive back through it self like a dual triode can. The Bassman preamp probably has more total more total gain because of the extra triode stage in the first 12ax7, the position number of which I don’t understand from your descriptions. Yes, there is nothing risky in cranking either preamp gain up if you want, but you’d need another internal tube stage to overdrive the EF806. Diming either amp will break up the amp section, especially with the low voltage point they run at. It should be even more noticeable with the Edge switch engaged.
An ET65(or 90) or Retro 30 will not start to break up until at least near their RMS power rating. If the amp section break up is too crunchy than you expect, it’s probably a combination of short plate PI tubes and the JJ KT66 power tubes. The JJ KT66 are more like KT88 – great for metal, but not like the original GEC KT66 at all. Do you even know if the power transformers can supply the full 1.3A for KT66 tubes? It can cause PT overheating if not. I’d try a pair of TS 7581A to compare either way. You might need those or some other 0.9A-rated 6L6 type with your PT’s.
To break in your speakers, you’ll need to crank the those amps near full power for many hours. There’s a way to use a Variac if you want to buy the ~$70 Chinese one online. Run it at ~1/3 the rated speaker voltage on either speaker out of the cab and leave it overnight. Look it up for more details, and use with caution. Hope we get to hear some clips at some point.
Ok so let’s do a quick recap of my shopping list here.
2 7581a power tubes for bassman.
2 ecc803s tubes [long plate] for Phase inv.'s
2 ecc83mg tubes for drivers.
1 ecc83mg for the bassman pre.
Never have purchased tubes other than a recto.
I know power tubes must be matched.
I am guessing I need the low harmonic low noise options for preamp tubes?
Do preamp tubes need to be matched?
Do I need to purchase “balanced triodes?”
Any other pro tips?
I meant to say Mids not kids.
Your tube purchasing recap is all correct. It should total ~$150, and the amps will be deeper with more low mid-emphasis and a smoother high end.
You might prefer a more mushy Sovtek 12ax7LPS in the PI of either amp, but they are more expensive. Maybe try one later.
The JJ ecc83MG is very low noise and has a more open high end than the short plate ecc83S. You may still prefer the darker/more-compressed ecc83S in the first or second stage of either amp depending on preference with a given guitar.
I’m wondering if the EF806 might be running in triode mode? That would substantially reduce output and dynamics.
Power tubes don’t have to be that closely matched, but matching doesn’t hurt.
Preamp tubes don’t need matching because they run in class A “series” mode. Balanced triodes are good for the PI stage for the intended performance, but are not necessary. It doesn’t cost much more anyway.
I’d buy the JJ’s from Eurotubes (for the best testing procedure), and get the TS 7581A pair from TheTubeStore as a matched set.
Last big tip is to use a low capacitance guitar cable for smooth extended highs. ~200pF can be good for a lot of things.
So I will say that just the new cabinet alone made a world of difference when it comes to the sounds I am getting here. I actually need more chime from the vox circuit now. I need to get the amp off the floor and get it up on a table because I am sure a mic would hear something different, it’s also worth noting that my practice space is small and has a bunch of concrete so… yes I will find a way to record it in it’s current state before I go making tube changes. Money is a little tight right now so In the meantime I am gonna get a blindfold and turn some knobs. I wanna see what I have in refrence to what I want before I go swapping because I dont throw money at the wrong preamp tubes. I do plan on grabbing the power tube (7581a) you have been raving about sooner than later, I also was wondering if you still recommend the 6ca7 for the vox side of the poweramp?
Yeah, you need to be within ~20d on-axis to a 12” guitar speaker to hear the 4kHz+ chime, so see what you think when it’s up closer to ear level – on the arms of a folding lawn chair like this?:
https://express.google.com/u/0/product/4981298279921624995_17973228280678435472_3766077?utm_source=google_shopping&utm_medium=tu_cu&utm_content=eid-lsjeuxoeqt>im=CJbQ9uvIxbzlMRDio7qhrLr5jHsY8PnPByIDVVNEKOCl--cFML3u5QE&utm_campaign=3766077&gclid=Cj0KCQjwocPnBRDFARIsAJJcf96Y9reRPDyWXH5P0Bar6CZhDV3xi5QKyUmJiXQNXwbDAFemiJWxbkUaAt4OEALw_wcB
Hanging a rug across even one wall can really help in an concrete room. Do two walls if you can. Across the corners is a good idea.
Preamp tubes can make at least as much difference as power tubes, and anyone I know of that’s tried the ecc83MG prefers them to the ecc83S. Use them in the PI too if the ecc803S is to bassy for you. Either way, I don’t think you can go wrong with those TS 7581A. The JJ 6CA7 are actually considered a relatively dark tube, so it depends what you think about the cranked amp sound when the speakers are up higher. You might even prefer the 7581A in the Vox side. My impression from reviews and demos is the JJ EL34II are more like EL84 than are the 6CA7, but I can’t really say what you’ll prefer…and you might find any EL34 too dark if the amp doesn’t have an EL34 impedance load option. Again, the PT must supply enough amps for EL34 types.
i found a pair of ruby 6l6gc laying around the basement, plugged those in and man that made a big difference from the kt66’s it sounds deeper, less woody than the kt66 (does that even make sense?) i have preamp tubes laying around but they are all just the same jjecc83s that is already in the socket unfortunatly. i havent tried the 6l6 on the vox side yet, just the bassman, but i am interested to see what happens, the highs are definatly more of an ice pick if i crank them through that 6l6. with some adjustment though i can make them sound closer to the fender clean i am looking for out of that bassman channel. i am still excited to see what that 7581 will bring to the table. i am admittedly toying with the idea of trying a set of kt88 in that vox channel too. they would give me more output than the 66’s and the 7581 too wouldnt they? ill play with that 6l6 in the vox side a little once the amp cools down again. if i like what i hear ill probably end up saving for a quad of those ts7581a tubes.
I think the Ruby 6L6GC are ShuGuang. Yeah, makes sense they are more lively, but harsher than the JJ KT66. I think the ShuGuang KT66 are sort of in between those two. You might like those in the Bassman side, but I think the preamp tubes I suggested would open up the sound with the JJ KT66 nicely.
There’s really no reason to order a quad of the 7581A without trying just a pair first – tube matching doesn’t apply to separate amps. KT88 might be worth a try, but I’d think the EL34II are more like EL84. They break up sooner than KT88, so they may actually sound louder at mid gain settings due to the the added harmonics and higher level average loudness. The EL34II have a smooth midrange and soft high end, while the KT88 are more crunchy. The JJ 6CA7 is cleaner and darker than the EL34II with a smoother midrange than the KT88. 6CA7 give a massive roar and chunk in a Plexi, but I think the JJ KT77 is the best of all worlds – fat bass, smooth mids, and sweet clear highs that get creamy when driven. They actually might be the best Vox side option, and an easy output match for the 7581A. Any power tube type will be darker and more distorted & saggy at the relatively low (~300V?) supply voltage, so cleaner fuller sounding tubes might make more sense. You can always set the Bassman side power switch to 1/2 if you need to. Either way, I wouldn’t order four power tubes of any type without first trying just a pair of something to compare to the JJ KT66.
Again, you should be able to split the Bassman side V3 driver and rewire the preamp inputs fairly easily if you want. A real Bassman just uses one driver triode per channel, and you’d have a triode with which to overdrive the EF806, for which you’d want an extra gain knob, maybe with a bypass switch. That would take some research, but I don’t think it’s that difficult. Otherwise, you might just consider a JJ 5751 tube in V3.
If you don’t want to spend quite as much on preamp tubes, maybe just order three ecc83MG and one ecc803S from Eurotubes (or The Tube Store) for a total of ~$60. Try the ecc83MG in V2 and V4, and in either V5 or V6, and try the ecc803S in the other PI slot – my guess is you’ll want it in the Vox PI slot to help mellow the high end and fatten mid-bass of the Retro 30. You could even order one JJ 5751 for V3 (instead of a third ecc83MG) if you know you want considerably less Bassman side gain. You can order another ecc803S later if you really want one in the Bassman PI slot. I doubt you’ll want to, but you could then use the extra ecc83MG in V3. As I said, preamp tube variants can make as much difference as power tube types, if not more. I’d do that before experimenting with power tubes so you’ll have a static reference point. You may even like the JJ KT66 just fine with those preamp tubes.
We are getting somewhat circular at this point. I think it’s time to take the plunge and try something based on what we’ve discussed thus far. BTW, have we established if the amp is cathode-biased? If not, you’ll need to rebias for different power tubes.
P.S. I didn’t originally recommend the JJ KT77 for the Vox side because I thought they’d be too clean and bright, but I forgot that your amp has a low supply voltage, so they are now my #1 Vox side pick. Probably the best sounding JJ power tube, and louder than the JJ KT66. Here’s a good comparison to the JJ 6L6GC and Mullard RI EL34 in a JCM800. Listen to how comparatively full, balanced, sweet and loud they are:
Here’s a comparison to the more-expensive/muddy GL KT77:
The JJ KT77 apparently have a grid leak resistance value limit of 250k compared to 500k for EL34, but KT77 were actually designed to run in a Ultra-linear circuit. I imagine the grid leak limit won’t be a problem since your amp is designed to accept all types of octal tubes – even less a concern if cathode-biased, which I’d think it is.