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Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Feb 5, 2019.
Warm glow on a very cold night.
At idle, this amp is dead quiet.
Finally got a chance to really run this thing through the paces. I used it Sunday at band rehearsal and was really able to let loose with it a few times since. I absolutely love the normal channel, both clean and wound out. The TMB channel is not getting my love... the lows are farty and it does not have much brilliance either. I ordered all new components for the front panel, maybe that will help. The pots in the recycled chassis don’t seem very healthy.
Wow, you brought an AK-47 to a knife fight!
So, I see grid resistors on some variants of the 18 watt TMB and not on others? Is this contributing to the "darkness" of this amp?
Depends on their value and I can read almost nothing in the image.
Post a high res version and I'm willing to do some calculations/simulations.
I believe there both 10K
They are 10K. I took them out last night so test the difference. I "think" it is a little brighter and I "think" it is a bit noisier without them...hard to tell not being able to A/B them on the fly.
I've never played through any 18watt variant before so have no frame of reference but a lot of people say that it can sometimes get too ice-pick-esqe, especially with single coils. I've been playing a Strat and Tele through it. On the bridge pickup, it's OK but not as bright as I want. With any other pickup combination, it’s VERY dark sounding and the bass is flabby.
Yeah 10K and people laughed at my clear back panel....... who’s laughing now
Interesting to see where this goes. I've never cranked mine up all the way. I always seem to be plugged in channel 2. I'm going to Crank it up monday neighbors are gone
I mostly use the TMB channel 2 as well.
Blencowe says 10k is the minimum input resistance that consumer audio gear expect to see. So I guess you should not remove it from the TMB input.
The high input on the other channel has a cutoff frequency of 20.4kHz with and 23.4kHz without the 10k grid stoppers.
I believe the low input will have an even higher cutoff frequency.
However... the 470k grid stopper of the second stage of the TMB gives a cutoff frequency of 3.4kHz.
Oh you'd know the bright 18w TMB tone if it was happening!
Are you still using that '51 Rola?
Might be the speaker that's dark and flubby.
I stick to the TMB channel on my 18 watters because the V/T channel is thin and lacks bass.
On the TMB channel with an Esquire I run the bass and treble both pretty low, like 9-11 oclock. That gets me a very bright tone!
With Celestion Gold or Red Fang which are bright but overall balanced speakers.
I find the bass of an 18w TMB with Fenders to be tighter than many similar small amps, tighter and more plentiful. A GB speaker gets looser bass, but still in a good throaty snarling way. Flubby bass is what I hear from a 5e3 or Princeton Reverb, and the reason I love the 18w is the bass is so NOT flubby.
If you're not using that vintage speaker I'm not sure what the problem is, but don't give up on it! Have you swapped the preamp tubes?
I forget, is V3 the first TMB tube and V1 the first V/T tube?
V2 being the driver on my TMB heads.
I almost traded some stuff on a VHT Standard 36 last year, but if they have crappy pots and jacks then maybe the price wasn't all that great.
Since I have three 18w I'm more interested in a 36 at some point.
Or just a JTM45/ 50...
The pots that were on the donor chassis were cheap and in very rough shape. I replaced them all with new and quality pots and it really brought the amp to life! I think the old pots were in such tough shape that they were not performing anywhere near their stated specs.
It still gets flabby on the bass when you push it. I’ve tried a couple different speakers from my organ donor pile...some are better than others. I have one more speaker to try that was pulled from an 18 watt Peavey Bravo that I’ll try next.
I had 1 more organ donor speaker to try. I was sort of hoping it wouldn’t be a good match because I have a pair of them earmarked for a different project. 1966 Jensen CR12. Haven’t pushed it yet but at lower volumes, the flubbiness is gone!
Yesterday at rehearsal, I got the speaker up off the floor onto an amp stand and was able to turn it up to live performance levels. All of my complaints are gone!!! This thing is glorious.
Next up...build an enclosure. I’m half tempted to build a combo enclosure and a new right-side-up (or would that be up-side-down) face plate but I’ll probably just stick with a head enclosure.
It really is a nice sounding amp.
Time for this thing to have a proper home. I found this head/1-12 cabinet kit at the local big box home improvement center.
I’ve assembled a few of their kits in the past and their quality gets a little better each time....they must sell a lot of these amp and speaker cabinet kits.
These kits from the big box store always require fitting and fine tuning. Glad I have this handy thing to hold the parts while I trim them to fit.
Now I’m thinking about slanting the front of the cabinet so that the top of the speaker is the same dimensions as the amp head. There’s 1-1/4” difference between them right now. I think it would prove useful and I think it might look less boxy that way...any opinions on that?
* Interesting side note... I built a combo cab one time to re-house a Peavey Bravo. Same dovetail construction as this set. The speaker baffle sat in a dato in the sides and bottom. I pounded it together with no glue, just how the parts fit, mounted the chassis and played through it for about a total of 4 hours at fairly high volume. It never did fall apart.
I’m going to cheat a little bit with the cabinet build and recycle this speaker baffle. It’s out of a Baldwin model 54 organ.
I’ll remove the grill cloth, trim 3 sides to make it fit the box, then re-install the grill cloth. This is exactly what I did for the 5E3 cabinet I built for my Spitfire project.
* Side note... the Baldwin model 54 is a gold mine! The amp has 2 amps running off 1 PT. The main amp is running 4 - 6BQ5 power tubes and 3 - 12AX7’s and the reverb amp is running 2 - 6BQ5’s and 2 - 12 AX7’s. I’ve salvaged 2 recently. One had a pair of ceramic Rola 12’s and the other one is where these Jensen’s came from.