Headroom & EQ help, PLEASE!!!

[DocRock]

Hey all,

I just recently made the switch from a Dual Showman Reverb to a Bandmaster Reverb. I'm running into an 8-ohm THD 2x12 cabinet. The reason I made the switch was because I found that I simply had to run the DSR way too loud to get anything out of the output section. I even tried pulling two of the 6L6's and that helped a little...but not enough. It was still way too loud, even for stage use.

I switched to the BMR because I liked the overall tonality of the amp, and found that I could get the output section to "give up the goods" at a much more reasonable stage volume. Still too loud for "bedroom" applications, but much better in a band setting.

Here's the problem I've run into. The BMR breaks up a little too easily, and while I like the tone, I find that it doesn't have the bottom end that the DSR had. I don't think I can go back to the DSR for the forementioned reasons. That had too much headroom, actually. I'm trying to see if I can get to a sweet spot in between the two extremes. Without doing any invasive mods to the amp's original circuit, is there anything I can do to tighten up the bottom end of the BMR, along with giving it just a tad more headroom?

Any input would be sincerely appreciated.

Thanks everybody,

Doc :)

[brad347]

buy the following tube types:

12AT7
12AU7
5751

Try swapping each of these into the first (or second, depending on which channel you use) preamp slot.

What kind of rectifier is in that amp?

If it is a tube rectifier and there is NOT a 5AR4/GZ34 tube in there (look at the actual tube and not just the tube chart) then try getting a 5AR4 tube and re-biasing your power tubes.

[brad347]

by first or second preamp slot I mean, facing the rear of the amp, the first two from the right.

The subs will change the tone and the gain to a degree.

The rectifier swap (if applicable) might be your best bet. Don't know when your amp is from but if it happens to have a 5U4 or something in there, going up to a 5AR4 and re-biasing will give you a touch more headroom and clarity, especially in the bass frequencies.

It also sounds as if your power tubes might be tired... if it already has a good rectifier, try swapping your power tubes and re-biasing.

Old and tired power tubes will often sound flubby in the bass and lose some power.

[DocRock]

Thanks so much for your response to my headroom/eq question about my Bandmaster Reverb. It's a 73-74 yearwise, non-master volume. Looks like the previous owner had already changed the rectifier tube. The chart calls for a 5U4-GB, but there's a GZ-34/5AR4 in there right now, with a pair of pretty new-looking Sovtek 5881-WXT in the output. Maybe the output tubes are too old. What do you like?

As for the pre-amp tubes, I had a 5751 so I tried it. It did help out a lot. I wasn't sure which slot to put it in, because I don't use the "normal" channel...only the "reverb/vibrato" channel. The tube chart reads, from left to right: 5U4-GB, 6L6-GC, 6L6-GC, 12AT7, 7025, 7025, 7025, 12AT7, 7025, 7025.

When looking at the back of the amp, there are 3 pre-amp slots on the far right, followed by a little square-shaped thing (looks like a miniature transformer or choke of some kind), followed by 4 more pre-amp slots in the middle, and then the 2 output slots and, on the far left, the rectifier slot. I took this to mean the the 1st three pre-amp slots (7025, 7025, 12AT7) were for the normal channel. Then, after that little square thing, the remaining 4 pre-amp slots (7025, 7025, 7025, 12AT7) were for the reverb channel. Since I only use the reverb channel, I swapped the 5751 into what I thought was "V1" of the reverb channel. Was that incorrect? Does the pre-amp tube farthest to the right govern BOTH channels? If so, then I guess that's where I'm supposed to swap? Or is my intuition of where "V1" of the reverb channel was correct?

Thanks again for your help...I really do appreciate it!!!

Doc :dude

[brad347]

Doc, see the PM I sent you. Second from right is the preamp tube for the reverb channel.

I recommend ditching the 5881s... see my PM

Good luck :)

[DocRock]

Doc, see the PM I sent you. Second from right is the preamp tube for the reverb channel.

I recommend ditching the 5881s... see my PM

Good luck :)

I'll check it out. Thanks again so much for your help!!!

Have a great weekend,

Doc :BEER

[deeval]

Try using the 2nd input on the amp,this is about 6db lower gain and then you can turn the volume level a bit higher and should give you extra head before breakup,also some speaker experimintation would help also.:JAM

[DocRock]

Try using the 2nd input on the amp,this is about 6db lower gain and then you can turn the volume level a bit higher and should give you extra head before breakup,also some speaker experimintation would help also.:JAM

Thanks so much for the tip!!! What kind of speakers would you recommend trying out? It's funny, the speaker does so much to give final shape to the sound, yet it's something I've never learned that much about. I'm not even sure where to start.

Anyway, thanks again!!!

Doc :dude

[deeval]

Depending on what type of music you are playing to achieve the tone you want.
You will have to try different spkers,I have experimented with alot of them to get the tones I want,Also have you tried using a quality amp attenuater to keep some of the headroom and being able to drive the amp harder?
It will take a few bucks and trial and effort to get what you want and then you will have so much gear you will be selling it after awhile.
Its becomes an obsession,and then you will still not be content.:horse

[DocRock]

Thanks, guys, for the valuable input! Another thing I had heard was that simply changing the output transformer to something a bit beefier could do a lot to tighten up the bass response, as well as improving the amp's overall overdrive response. A couple different people suggested changing the Bandmaster OT to a Bassman OT. I've read posts from other BMR guys who have done that and never looked back. What do you think of that idea? Seems like it would be pretty inexpensive to do. I've heard good things about Heyboer. Any thoughts?

Thanks again,

Doc :)

[donnyjaguar]

Isn't the bandmaster the one with the small output transformer? If so, the reality is there just isn't enough iron, and resultant magnetic permiability, in the output tranny to properly amplify the lower-frequencies. Swapping tubes and speakers is only going to bring a little symptomatic relief. I'm considering doing this swap with one of my under-tranny'd heads. The dilemna is, do you spend money to modify it to make it more useful and then risk reducing its collector value?

[DocRock]

Isn't the bandmaster the one with the small output transformer? If so, the reality is there just isn't enough iron, and resultant magnetic permiability, in the output tranny to properly amplify the lower-frequencies. Swapping tubes and speakers is only going to bring a little symptomatic relief. I'm considering doing this swap with one of my under-tranny'd heads. The dilemna is, do you spend money to modify it to make it more useful and then risk reducing its collector value?

Thanks for the input!

I see what you mean about the collector value. I'm going to hang on to the original wimpy OT in case I ever decide to sell the amp. But in the meantime, I am gonna try and make this thing more useful to me, as I do gig with it.

What do you think of Heyboer products? Any knowledge or experience with them?

Thanks again,

Doc :)

[brad347]

I recommend a few extra $$$ for a Mercury Magnetics transformer. You won't look back, and even "vintage amp snobs" tend not to frown when they see a MM tranny in there...

[DocRock]

I recommend a few extra $$$ for a Mercury Magnetics transformer. You won't look back, and even "vintage amp snobs" tend not to frown when they see a MM tranny in there...

Hey Brad,

Thanks again for your responses. This whole techical discussion of swapping OT's is *very* new to me. I've been going largely on what I've been hearing. Some have said that MM is the best money can buy, some have said MM is overpriced. I haven't heard anything bad about Heyboer yet. I did some pricing on the net, and noticed that the MM costs DOUBLE what an equivalent Heyboer would cost. I realize tone is a very subjective phenomenon, but I wonder if MM sounds twice as good as a Heyboer. Do you have any experience with Heyboer? Is it good stuff?

Thanks,

Doc :)

[brad347]

I don't have much experience with heyboer. I'm pretty sure that the MM probably doesn't sound "twice as good" even though it IS "twice the price."

It all depends on you. I'm a perfectionist, I would always spend more to get a sound that was even a little bit better.

Do you know how they Heyboer trannies are made? Interleaved, etc?

[DocRock]

I don't have much experience with heyboer. I'm pretty sure that the MM probably doesn't sound "twice as good" even though it IS "twice the price."

It all depends on you. I'm a perfectionist, I would always spend more to get a sound that was even a little bit better.

Do you know how they Heyboer trannies are made? Interleaved, etc?

Well, the Heyboer site sucks. It has almost *ZERO* information on it. I'm told that they're made the "old school" interleaved, paper bobbin style.

[brad347]

interleaved paper bobbin... probably a ok.

[DocRock]

Thanks again, Brad. I'll post once I've done the tranny swap and let you know how it turned out.

Best,

Doc :dude

[brad347]

good luck! I'd love to know how it turns out.

[Shea]

Heyboer trannies are good. They recently wound me a replacement OT for a Fisher stereo, and it sounds just as good as the remaining original one.

One potential drawback to putting a Bassman OT in a Bandmaster Reverb is that you'll probably have to drill extra holes in the chassis, unless you can fabricate some kind of adapter plate.

Shea

[John Phillips]

If you haven't bought the new transformer or drilled the amp chassis yet, try using JAN/Philips 7581A tubes. These are a drop-in replacement and at most will need a rebias (but maybe not, check first - they're also rated at 35W not 30 like the 6L6GC so they can run a bit hotter without problems). This won't achieve as much as fitting a Bassman OT, but it will increase both headroom and low-end, is cheaper and doesn't involve modding the amp.

If it isn't enough you can still fit the new OT and run the 7581As - you'll get a really big tone like that.

Another option is to use more efficient, tighter-sounding speakers... something like JBLs. You'll achieve more like that than even by replacing the OT.

[DocRock]

Thanks everybody for all the input. John Phillips, I'll look into the 7581A idea. I've never heard of those tubes, but I'll check them out....

Best,

Doc :)

[DocRock]

Okay, here's a question. I got the Heyboer (via Mojo) Bassman OT today. It has 2, 4, and 8 ohm taps on it. I don't want this amp to be totally clean like the DSR I had, so I have kind of enjoyed the break-up I've been getting by running the BMR (which wants to see 4 ohms) into an 8 ohm cabinet. Since I'm using an 8 ohm cab, should I use the 8 ohm tap on the new OT, or will that make the amp too clean? Am I better off using the 4 ohm tap (as it was designed) and then continuing to run it into an 8 ohm cab to keep some of that extra distortion I'm getting from the impedance mismatch? I like that the BMR breaks up around 5 or so. My main (and original) complaint was the flabby bass, which the new OT ought to fix.

Any further thoughts?

Thanks again,

Doc :)

P.S. I know, I know: :horse

[Shea]

I would use the 8 ohm tap, and if the amp isn't distorted enough for you, then reduce the negative feedback.

If it's a 70's BMR, converting the phase inverter circuit to blackface specs will get you more dirt too.

The problem with using a speaker impedance that's too high is that you could get arcing at the tube sockets. That will lay down a trail of carbon between the two pins where the arc occurs, and then you have to replace the socket.

Shea

[brad347]

+1 what Shea said.

[DocRock]

Thanks, I'll take that under advisement. I hope I'll be able to return the favor and help you guys out one day....

Have a great weekend!!!

Doc :dude

[DocRock]

Did the swap on Saturday...so far so good. I had my guy wire it so that one speaker jack uses the 4 ohm tap and the other uses the 8 ohm tap...that way I still have a choice. I'm using the 8-ohm tap as advised wtih my 8-ohm cab. Sounds really good. I still don't run the bass past about 2 1/2, as the overall tonality of the amp gets kinda boomy. I hear that old Fender's are notorious for being bass-heavy. That being said, the quality of the bass is way tighter. No where near the fartiness it once had. Overall, I think the Bassman OT swap was a good move. I wish I could dial some of the "ice-pick" out of the amp, but maybe that's what happens when you spend less than a grand on an amp...I don't know. It could be an inherent design flaw, tough to say. Overall I'd say I'm pretty happy.

Thanks again for the advice!!!

Best,

Doc :)

[Han Solo]

This has been mentioned before but try some different speakers. My BMR sounds great with some efficient Weber speakers, and does not have the "ice-pick" at all.