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Discussion Starter #1
I am looking for ways to quiet down my YBA-1 while hopefully getting a bit of poweramp grind out of it, in other words a straight Volume control in front of the poweramp isn't really what I am looking for.

So far for about the same price I see a Weber mini mass 50 and a London Power - Power Scale Kit. both less than $200.

Does anyone have experience or comments on either option?
Any other suggestsion are welcome. thanx.

Mark.
 

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The weber mini mass is just an attenuator but it has some nice features.Power scaling,while the KIT may be the same price,it requires a very experienced tech to install it for you.It takes up space inside an amp and it creates heat which needs to be disipated somehow.
You can also build your own attenuator for about 50.00 using a 100 watt L-Pad.Easy peasey.

www.claramps.com

[email protected]
 

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Discussion Starter #3
Hot Hot Heat

I hadn't considered the heat thanks, I have a feeling it wouldn't fit in my head anyways.

I never thought about building a pad - a quick google search brings up this link for rolling yer own.

http://www.webervst.com/lpad.htm

looking at it closlely it's nothing I didn't learn in first year Electronics. Sometimes I forget and get all caught up in the snake oil sales pitch!

Still curious to hear from people who have tried different options.

Mark.
 

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Well, I was just about to chime in and say that my tech just installed 6V6s in my bassmaster to help bring down the volume.

Guess who my tech is . . . (hint, he replied to your thread already!) :)

TG
 

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I've got a Webber Mass 100. It does the job very well. I have found my sweet spot for bedroom use but not yet for gigging volumes.

I plugged into my amp un-attenuated for the first time in months and wow! My amp definitely sounds better without it...........but its damn loud! :rockon:
 

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Well, I'm a big fan of power scaling and have been using power scaled amps for 3-4 years now. I really can't imagine using an amp without this feature now.

IMO, the technology works great and allows you to get nice power tube distortion at pretty low sound levels.

That being said, I only have experience with amps that were designed to incorportate the technolgy (i.e. Stephenson and London Power). I'm not sure if the results would be the same with a retro-fit.
 

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Discussion Starter #7
TG - those 6V6's sound interesting , what's the rated output of your amp now? - I'm gonna take a wild guess your amp tech is Kevin?

ne1roc - are you able to use the high and low attenuation settings on the Wevber to dial in a fairly neutral tone?

Scottone- thanks for the reply - can you describe in general terms what this Powerscale technology is doing? I'm jjust curious and I'm not interested in reverse engineering at all. I can't really tell from the London Power site what it's all about.


If anyone has experience with aTHD Hotplate or Dr. Z airbrake I would be interested in hearing comments.:rockon2:


Thanks for all the replies,
Mark.
 

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I have a Weber Mini Mass that I used to use with my Superbaby. It did work, but... it really sucked some of the tone out of the equation. I tried it with my Valve Jr. and my Fender Blues Jr. - same thing. It does do the job... but for me the tone sacrifice just isn't worth it. Just my 2 cents.
 

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Telemark said:
Scottone- thanks for the reply - can you describe in general terms what this Powerscale technology is doing? I'm jjust curious and I'm not interested in reverse engineering at all. I can't really tell from the London Power site what it's all about.
Mark.
There are two controls..

The scale is basically a variable AC regulator connected to the high voltage winding of the P/T. The regulated AC is fed into the rest of the power supply. I know that it can be wired so that only the power amp is scaled, or other stages can be scaled as well.

The limit control controls the amount of signal fed from the phase inverter to the power amp (can be implemented as a Post PI Master volume or through other methods)

Kind of the same idea as using a Variac, but 6.3V and 5V filiment supplies aren't affected and you can tailor which parts of the circuit get scaled.

It's actually a pretty simple idea that works really well in my experience.

Hope that helps...

Scott
 

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Telemark said:
TG - those 6V6's sound interesting , what's the rated output of your amp now? - I'm gonna take a wild guess your amp tech is Kevin?
Yes, Kevin (aka "addicted to tubes, aka Clara amps) did the work so he can give you a more technical answer. I would imagine two 6V6 would be putting out around 20-25 watts so the amp is basically about half power. Mine is an old unit with a tube rectifier.

When the amp was running 6V6 I couldn't even get the amp to break up without people (even a drummer!) telling me to turn it down. The amp sounded amazing, but was too loud to be useful. If I was running a two amp setup (one clean, one for dirt) I would have left the amp with the 6L6s but I don't want to lug all that gear to a jam.

The amp should arrive tomorrow so I won't get a chance to crank it up for awhile.

TG
 

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Telemark said:
I am looking for ways to quiet down my YBA-1 while hopefully getting a bit of poweramp grind out of it.

Does anyone have experience or comments on either option?
Any other suggestsion are welcome. thanx.

Mark.
I use a 'bridged attenuator' with my epi valve junior and pignose gt40.
I run the Vjr wide open.
After the attenuator I have an L-pad, which is really just a 8ohm variable resistor and I've put a 2.2uf non-polarized capacitor as a high frequency bypass across the L-pad.

The 'bridged attenuator' is described here;
http://www.18watt.com/modules.php?name=Downloads&d_op=viewdownload&cid=38

schematic is;
http://www.18watt.com/storage/bridged_t_schematic.gif

R3 and R4 are always equal to your speaker impediance, so in my case both are 8 ohm ten watt resistors. ( about 1.80 each ).
Currently I'm using a 76ohm R2 and a .68ohm R1 both ten watts.
I would describe this as loud-ish, suitable for daytime, not suitable for nighttime.
So the L-Pad makes for the final adjustment from silent to loud-ish.
Last week-end I bought a few more resistors and a switch so I am going to find three settings that I like.
Here is a spreadsheet of the required values for different dB reductions for 8ohms.
db R2 R1
10 17.30 3.70
11 20.39 3.14
12 23.85 2.68
13 27.73 2.31
14 32.09 1.99
15 36.99 1.73
16 42.48 1.51
17 48.64 1.32
18 55.55 1.15
19 63.30 1.01
20 72.00 0.89
21 81.76 0.78
22 92.71 0.69
23 105.00 0.61
24 118.79 0.54
25 134.26 0.48

You can see that I'm around the 20db mark.

I'm quite happy with it.
I can bring back the highs so I'm ok on that.
Really it is for late night playing and it works great for that.
With the Valve Jr un-modded the resistors stayed cool.
With the Valve Jr modded the resistors get warm.
With the 40watt Pignose the resistors get hot.

I would like to try a minimass as well, I havent found a used one yet.
 

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Discussion Starter #12
Easy Peasey

I use a 'bridged attenuator' with my epi valve junior and pignose gt40.
I run the Vjr wide open.
After the attenuator I have an L-pad, which is really just a 8ohm variable resistor and I've put a 2.2uf non-polarized capacitor as a high frequency bypass across the L-pad.
Thanks for the great post Jxoco. I have been searching the 18watt site for more info and searching the web for LPADS - where did you get yours? and why did you choose LPAD plus Bridged T? I'm thinking that is a pretty versatile option but I haven't seen anyone else use it.

traynor_garnett - let us know how those 6V6's sound. I think I am going to go this way if I can get my plate voltage low enough, still need to figure out how low that is! Maybe I can change my rectifier... this sounds like a great option.

Scottone - Thanks for the info, I am going to look into powerscale for some future project, I think an 18Watt is next though!

Tarbender - I would expect an attenuator to mush up the signal at bedroom levels - have you played at a giggin level with a drummer? just curious.


Thanks everyone for all the great posts.

Mark
 

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Telemark said:
Thanks for the great post Jxoco. I have been searching the 18watt site for more info and searching the web for LPADS - where did you get yours? and why did you choose LPAD plus Bridged T? I'm thinking that is a pretty versatile option but I haven't seen anyone else use it.

Mark
I had bought the 'L-pad', actually it is just an 8ohm pot, years ago.
Although it is pot shaped and has the normal 3 connections, the marking on it is 8ohm 1.5amps. To me that is 18watts. So I've used it on lots of things.
When I got the Valve Jr I realized that I don't have to worry about the thing burning up anymore so I just started running the Valve Jr. wide open all the time and controlling the volume from the 'L-pad'. But it is touchy. A tiny move on the knob makes a big change at the speaker. Only the last 1 degree of movement of the knob did everything.
So I thought the Bridged T would knock it down pre L-pad. And it does just fine. With the resistors I first bought I have about 90 degrees of adjustment on the L-pad. I'm going to try to refine that with some other values of resistors. And rather than bringing the highs back from the input of the Bridged T, bringing them back from the top end of the L-pad pot to the wiper sounded better to me. That may change if I get too many degrees of adjustment. Right now it's picking off the signal probably 4ohms away from the wiper.
It has just been an experiment that seems to work well for me.

If you do a google search for valve junior there are another couple of sites that have people using radio shack L-pads that are just big pots and an L-pad that home depot sells that has transformers that knock the sound down and one guy has wired a light bulb in series to reduce the volume.
 

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Telemark said:
[
traynor_garnett - let us know how those 6V6's sound. I think I am going to go this way if I can get my plate voltage low enough, still need to figure out how low that is! Maybe I can change my rectifier... this sounds like a great option.
Mark
Is your head running a tube rectifier? If so, you should be fine because I believe the earlier heads don't run as high. New JJs 6V6s can really take a beating, but again, you should talk to Kevin for the details (though he would have chimed in by now).

TG
 

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Discussion Starter #15 (Edited)
Is your head running a tube rectifier?
yup I have a tube rectifier but can't remember which type (maybe a 5ARA4?)- all my notes are at work. I haven't looked into these yet, my tube amp tech skills are sllllooooowly coming around, after 20yrs of thinking I should give it a try one day!

I'm not sure of these rectifier tubes yet, but I 'm sure a little research will pay off.....wait, now I know they are full wave rectifier devices and what's this some voltage drop specs!

swiped from http://www.guitaramplifierblueprinting.com/rectifiers.html

Typical Rectifier voltage drops

5Y3 -60 volts @ 125 mA
5U4GB -50 volts @ 275 mA
5U4 -44 volts @ 225 mA
5V4 -25 volts @ 175 mA
5AR4 -17 volts @ 225 mA

looks like could lower my plate voltage by changing to any of these rectifiers!

I think this is looking good maybe a 5u4 or 5Y3 plus 6V6's and a switched bridged T pad,

Edit for extra info: My online notes from the YBA-1 thread show my plate voltage at 468 Volts! I think this is too high for 6V6's n'est-ce pas?

Mark.
 

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Discussion Starter #16
JROBERTS:

The Dr. Z Airbrake is the only attenuator I have experience with. I love it. But, I'm just attenuating from gigging volumes down to rehearsal volumes. For band rehearsals, the Airbrake is on. Then I take it off for shows, and everything sounds pretty much just like it did in practice, but louder. I havn't really tried "bedroom" volumes with it, though.

Davetcan posted a clip of a friends Traynor with an Airbrake - it sounded really good. Thanks for the Info.
 

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Discussion Starter #17
In the Name of Attenuation...

While I wait to see if anyone thinks I am over my head with all this new found info - enuff to be dangerous -

I am about to buy an AY7 for my V1, a matched pr of JJ6v6s - from the Tubestore. I am also going to change my screen resistor to a 1K (from 470) before installing the 6V6's.

What I am wondering is should I try a 5R4 to lower the B+ or just stick with the 468volts???

Maybe it's time for a new Kevin O Connor Book!

Cheers. Mark.
 

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Fyi

Telemark said:
While I wait to see if anyone thinks I am over my head with all this new found info - enuff to be dangerous -

I am about to buy an AY7 for my V1, a matched pr of JJ6v6s - from the Tubestore. I am also going to change my screen resistor to a 1K (from 470) before installing the 6V6's.

What I am wondering is should I try a 5R4 to lower the B+ or just stick with the 468volts???

Maybe it's time for a new Kevin O Connor Book!

Cheers. Mark.
I would be careful using a 5R4. It has a limit of only 10 mfd for the 1st filter capacitor. Empty filter caps look like a dead short when they first start to charge up. For that split second the rectifier is essentially feeding into a short and this stresses a rectifier. That's why we see much higher values of filters with modern silicon diodes than with tube rectifiers. Good data sheets will warn you with tubes like the 5R4.

If you're running choke-input the choke limits the initial surge of current and you can run higher values.

When you're looking for a tube rectifier with enough voltage drop remember that they drop less at idle currents than at full draw. You do get a break if you want to run those 6V6's with cathode bias. Fender ran 6V6's with about 410 volts on amps like the Deluxe Reverb. I've used modern 6V6EH's with never a problem. With cathode bias you can subtract the cathode bias voltage from the plate voltage reading to ground to find the actual B+ ACROSS THE TUBE! We often forget when taking voltage readings using ground as the negative point that a tube is rated by voltages from plate to cathode. It couldn't care less if the cathode is grounded or is raised up by a cathode bias resistor, just the difference from plate to cathdode.

A 5Y3 is most often used with 6V6 amps. If when you measure the plate voltage after plugging in the smaller tubes and think you need another 20 volts or so less B+ to be safe then consider throwing in a 250 ohm/10 watt shared cathode resistor with a suitable cap bypass. You might have to play with the resistor value a bit to get a suitable idle current. If you need any help with that then check back here.

Cathode bias has a GREAT rockin' tone!
 

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I don't think my rectifier tube type was changed so you may not have to bother with this. (Freakin Canada Post, deliver my amp already!!!!!)

TG



Telemark said:
While I wait to see if anyone thinks I am over my head with all this new found info - enuff to be dangerous -

I am about to buy an AY7 for my V1, a matched pr of JJ6v6s - from the Tubestore. I am also going to change my screen resistor to a 1K (from 470) before installing the 6V6's.

What I am wondering is should I try a 5R4 to lower the B+ or just stick with the 468volts???

Maybe it's time for a new Kevin O Connor Book!

Cheers. Mark.
 

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Power Attenuator

I did the whole load box thing 3-4 years ago. There are several good ones on the market... Weber, Rockman, THD, Koch.
I went with the Koch... it sounds great and is priced fairly. The only thing I'd like to say is... IMHO... buyer beware on the Marshall Load Brake.

Khingpynn
 
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