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Bitmo voicing /gain switch question ???


2blu4u

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I am installing the Bitmo voicing/gain switch in my V-JR. version3.I want to know which nib next to the preamp tube socket I should solder the wire from the caps to,as they are not labled.The one closest to the socket?Also the wire between the caps- Should it be soldered to the middle nib? This is my first time trying any mods so any help with this would be greatly appreciated.

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Mods tend to change a little from time to time, so you might want to consider sending an email to Bruce directly with questions qualified for BitMo tech support. He the one person most likely to know exactly what you're asking about.

 

Gil...

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Thanks for the reply.I have contacted Bruce and he told me to wire the cap side of the switch the version2 way.I was having trouble getting to the solder points that way. I ended up taking the volume swich out for better access and was able to get it soldered. Fired it up and everything works fine. Sounds great! Next, the Hammond 125DSE.............

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so maybe I wanna do the Hammond 125DSE too... my VJ has the Brite, Gain and Standby - is the transformer swap all I have to do or is it "more involved" than that. I bought mine "modded" already - I'm not really an electronics type although I do AC Electrical (110/220) stuff daily. Where's the info? And Let me know how it changes the sound...

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Swapping the OT has been generally considered the easiest mod you can make to the VJr.

 

The Hammond OTs are more efficient than the stock OT, so voltage to the plate of the el84 will go up. Chances are, it's already too high. Add in the fact that the bias resistor is a little too low which causes the el84 to dissipate more power than it's spec'd for, it's no wonder those amps eat tubes the way they do.

 

If the voltage you get at the wall runs higher than normal, then yes, you should definitely get the B+ rail voltages and the bias under control. If you intend to swap OTs, it's better to adjust the rail resistors after the swap, so you don't have to do it all over again.

 

The BIG question, is, SHOULD you swap OTs? If you have a v3 VJr, then no. Even a Hammond 125ESE won't be much of an improvement. Think tiny bang for very big bucks. If you have a v2 or v1 VJr. then definitely YES. any Hammond OT will be a huge improvement and the biggest bang for the bucks possible.

 

Gil...

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I already have the 125DSE. Being a newbie, I would not know the wall from the ceiling or the B+rail from the A train.

So the question is-Will it hurt the amp to install it? Even if the benefits are small, I am having fun playing around with this thing. Thanks.

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You should get a meter and test your voltages.. and maybe swap a component or two out so you are getting the sweet spot, not overheating anything. stuff like that.

you can bias a tube hot or cold.. with varying results..

you can have your heaters too high and wear your tubes out too soon.. as well as affecting the sound.

but it's not rocket science, it's more like Mr. Wizard with a little more patience and less of a desire to blow things up.

plenty of help in here and at many websites.. just keep asking.

 

TWANG~

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I have a multi-meter but I'm not to experienced with it. Anyone feel like walking a mental midget through this thing?

What do I set the meter on and where do I check these voltages? Also what safety steps do I have to take so I dont get knocked on my butt or worse? I have completed the Bitmo Trio mods, and am about to swap the OT.

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Eurotubes has a bias tool you can use. As I understand, replace the EL84 with the meter and fire up your amp, write some numbers down, solve E/(I*R)=1, solve W(E)=E*I for E where W=12, solve E®=I*R for R with the found E value, drop in a resistor of value R.

 

Tung??? Your thoughts??

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First of all, what type of meter is it? Can you post a link to a photo so I can advise you exactly what to set?

 

Generally, setting bias in a VJ involves setting your meter to measure DC voltage. Some meters have auto ranging built in so you don't have to keep changing the range to measure voltages, i.e., 10v for the cathode to ground, 300v+ for the anode to cathode voltage.

 

You definitely want to invest in a set of retractable hooks for your meter. These fit over the probe tips to make it safer to take readings.

 

Here are some instructions for setting bias I have on my web site:

 

http://www.diycustomamps.com/valvejunior.htm#vjbias

 

If anything is unclear, let me know and I'll try to help you through it.

 

tung

 

 

 

I have a multi-meter but I'm not to experienced with it. Anyone feel like walking a mental midget through this thing?

What do I set the meter on and where do I check these voltages? Also what safety steps do I have to take so I dont get knocked on my butt or worse? I have completed the Bitmo Trio mods' date=' and am about to swap the OT. [/quote']

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Eurotubes has a bias tool you can use. As I understand' date=' replace the EL84 with the meter and fire up your amp, write some numbers down, solve E/(I*R)=1, solve W(E)=E*I for E where W=12, solve E®=I*R for R with the found E value, drop in a resistor of value R.

 

Tung??? Your thoughts??[/quote']

 

Damn I knew I shouldn't have skipped so many classes... I DIDN'T KNOW THERE WOULD BE MATH! I guess I'll leave the "tweaking" to you guys and I'll just wank on mine like it is. ](*,)

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Thanks Tung. I dug out the multimeter. Its a Fluke 77. Went online and downloaded a manual for it. I need to find someplace to get some retractable hooks. Any suggestions? Was thinking about swapping OT following the thread a couple above this, but wondering if I should get any readings first.

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I've got a couple pages on how to do this.. I'll scan them and copy paste later on today when I have time.

 

It'll tell you how to hook up.. alligator clip to the ground lead to the amp.. red or hot probe to test points..

and it gives you what voltages to look for etc.. can't remember where I got it, or I'd just pop in an url.. probably came from one of the threads

in here or elsewhere..

 

you want to get your tests done.. swap the ot.. then retest.. that ought to tell you what you need to bring it up to snuff, pretty easily, really.

 

I'm not a math guy either, and this has worked for me perfectly well.

 

TWANG

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Thanks Tung. I dug out the multimeter. Its a Fluke 77. Went online and downloaded a manual for it. I need to find someplace to get some retractable hooks. Any suggestions? Was thinking about swapping OT following the thread a couple above this' date=' but wondering if I should get any readings first.[/quote']

 

Okay, I took a look at the 75/77 manual, and if this is the same one, it looks like your meter is auto ranging. Just set the selector to VDC. Put your black probe in the COM jack, and put the red probe in the V? jack.

 

Fluke is a highly regarded, well established brand, you will most likely be able to find retractable hooks locally. Check in the Yellow Pages under "electronics." Failing that do a Google search.

 

I found these on the MCM Electronics site:

 

http://www.mcmelectronics.com/product.asp?product_id=58-9915&catalog_name=MCMProducts

 

I don't know if they'll fit your meter, but you could call customer service and ask.

 

tung

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Dude, you're making that way too hard O:)

 

Here's how I remember it: "current equals voltage divided by resistance" and "dissipation equals current times anode to cathode voltage."

 

Math never was my strong suit, I barely passed high school and college algebra. :-

 

tung

 

Eurotubes has a bias tool you can use. As I understand' date=' replace the EL84 with the meter and fire up your amp, write some numbers down, solve E/(I*R)=1, solve W(E)=E*I for E where W=12, solve E®=I*R for R with the found E value, drop in a resistor of value R.

[/quote']

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O.K.- I took some readings following the diycustomamps site. R-14 is 215.5 ohms. Cathode voltage is 11. Cathode to ground is 339V, subtracting 11=Anode to Cathode of 328V. Cathode current is .051. I dont understand all the stuff about dissapation. I will swap out OT this weekend and get new readings. Hopefully, you guys can help me with biasing. Should I solder all the OT leads, or are crimp on quick-connects allright? Also I have read something about bleeder resistors in this amp.Does this mean it is drained of voltage after being turned off for a time? If not,what is the easiest way to do this? Thanks

 

 

2blu4u

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Well I swapped the OTs and took new readings. Anode to cathode went up to 336. Multiplied by .051, Dissapation is 17.1w. Do these numbers seem in the normal range? If not, what should I change? Sounds O.K., but seems to break up too early.

Thanks,

2blu4u

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