Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: lego4040 on January 05, 2018, 06:38:07 pm
-
So work let this one go on Wednesday, they werent sure if it was working. So i opened up and seems its been worked on before, All values are good except R7(365ohm). Aside from me knowing they are 1% resisters I am not sure what wattage to use? The part # from manual is 15K-8450UC5. Im sure its above 1Amp but voltage handling needs to be up there as well(600Volts+?) This is high voltage capable.
-
One watt will be fine. R7 is only used on the OHMS function so the only voltage it will ever see is the internal battery voltage. The part number you posted is for R10, not R7.
There is no replacement for that 30 volt battery. But that only affects the R X 100000 scale. Three 9 volt batteries connected in series works just fine. There is a youtube video that shows this...
-
Thanks the correction Steve, Ill order that here if Doug has it. I have a parts list saved and ready to put in. I decided a 50 watt Marshall would not be appriciated in an apartment building so Im gonna build the Princeton Reverb
-
Nice meter! If you want, there are 30V batteries on eBay, I've got a couple and they work and hold up just fine (so far)
https://www.ebay.com/sch/i.html?_sacat=0&_nkw=413+battery&_frs=1
If you find that meter does need work and don't mind spending a little money, there's an outfit in CA that does outstanding work. Meter Specialists, I think they're called.
-
:huh: Almost 30.00 for that Battery. All the other resistors and diodes tested good, there was a 1.5 amp 200v fuse instead of 1 amp 600v. Ill swap out bad resistor, use 3 9volts and go from there. Thanks for that link
-
Don't waste time looking for this resistor at guitar amp suppliers. Go straight to Mouser. I'd get this one...
https://www.mouser.com/productdetail/vishay-dale/cpf3365r00fkb14?qs=sGAEpiMZZMtlubZbdhIBIMqLHvoLXMI%252bd9GFuUivBH8%3D
-
https://www.ebay.com/itm/2Pcs-10F20-15V-Dry-Battery-220A-B154-DH554-GP220-for-Voltage-Analog-Multimeter/322913291078?hash=item4b2f21cb46:g:uxQAAOSwh6xTumQQ
-
:icon_biggrin: Thanks for coming through guys. R5 is toast too, and the probes arent the correct ones either. I’ll print out the manual at work tomorrow, dont want to waste my paper at home. Those batteries are something else. I got a order almost ready to go in tonight to Doug for a new BFPR. I will post a pic of how P2P did a cocentric bass/mid pot Id like to do
-
Alright, so many little things going on. I have the mouser part in my cart, thanks for link Steve. One more resistor I have to replace is R5 which is a 3.55ohm. The closest thing I can find in 1 watt is this https://www.mouser.com/ProductDetail/KOA-Speer/MOX1C3R6J?qs=sGAEpiMZZMvmQ%252bOLa8n%2fM5uRxY2%252b5i%252beiqyYoh%2fhxZM%3d (https://www.mouser.com/ProductDetail/KOA-Speer/MOX1C3R6J?qs=sGAEpiMZZMvmQ%252bOLa8n%2fM5uRxY2%252b5i%252beiqyYoh%2fhxZM%3d) or this S.M.D. which is even closer at 1% tolerance. I suppose I can just solder onto leads or make a small pcb board for it https://www.mouser.com/ProductDetail/Vishay/CRCW25123R57FNTG?qs=4PLzlLprOt4gzwQ8y3S%2fmg%3d%3d
-
Replacement resistors are on the way and hopefully with quick fix I can have it running. Now should I not have this up and running is worth to send out for refurb? It has no sentimental value other then I got for free. If I wanted to grab a working vintage like this one what is a good option. I would of coarse try and get one that has been tested and calibrated. Simpson 260 and the Triplet 630 seem to be the most I see on the net although I did see a cool looking Heathkit
-
I use 4X Heathkit IM-18 VTVM's. There are similar Heathkit models; also Eico & RCA. They're all good and working units are available.
-
I'll check those out, I have my Dads Lafayette from when he was in High school that works. My thing is my eyesight, I'm hitting 50 and my eyesight is going to shit lately. I need progressives now and the bigger numbers the better
-
Eico makes a model with a huge meter display. So does RCA called the Senior Voltohmyst; and others.
The later model VTVM's, regardless of brand, all use the same basic circuit. Tube types may differ. It's a bridge circuit that self-compensates for differences in wall supply voltage, and different performance as tubes age.
The vintage manuals are fantastic, like Heathkit & Eico. I didn't get into electronics until about 2004, so I missed the '50's & '60's. Today's revelations were common knowledge back then. Also, the Heathkit & Eico operating manuals were for kits so they also showed in plain detail how to assemble these things, with detailed instructions on how to solder, etc., etc.
Checkout:
http://tone-lizard.com/vtvm-advertising/ (http://tone-lizard.com/vtvm-advertising/)
https://archive.org/details/ServicingRadioAndTelevisionWithAVacuumTubeVoltmeter (https://archive.org/details/ServicingRadioAndTelevisionWithAVacuumTubeVoltmeter)
You can google the latter & download the PDF for free
-
:worthy1: Now thats what I am talking about on Tone-lizards site. Gotta keep an eye out for one of those. Thanks for the link, so many damn things going on its like Ill never get done. This afternoon my little apprentice is helping me get some more time out of our 1950’s table. Then rearrange dining room, maybe Ill get some soldering done on Princeton tonight :dontknow:
-
She's adorable!
Glad you liked the vintage VTVM ads, but I meant to post this: http://tone-lizard.com/vtvms/ (http://tone-lizard.com/vtvms/)
-
She is, she helped me most of the day but had to take ntesks when she got bored. I replaced the resitors and the x1 and x10 was not well i couldnt Zero them out. The neddle only went across the meter 3/4th of the way. All the other ranges where spot on. Ill do more research, maybe look for local repair shop. I read the tone lizard link you meant, I will read that a few more times with a circuit in front of me. Ill also look at the vtvm’s
-
:icon_biggrin: I’ll print out the manual at work tomorrow, dont want to waste my paper at home.
I hope your boss doesn't read this thread. :l2:
-
I stay away from printing the big files or print out on the old paper with funky colors. I did just go to my local and request two books they had for begineer/understanding scopes. What I usually do is create my own manual, I use composition notebooks and rewrite and draw in terms i can understand. Having ADD sucks, Im always doing multiple tasks and the only way I was able to study even when I was in school was to Read, brake it down into facts and write it into another book, while listing to music. If I didnt my mind would be off riding a bike :laugh:
-
Having ADD sucks
I'm the poster child for ADD :icon_biggrin:, add dyslexia, (numbers, letters, AND speech(you "flip words" as you talk)!
the cool thing, I was born before they started labeling me, so I excelled at ANYTHING I put my unique mind to :icon_biggrin:
-
My wife always asks when I am multitasking, did you take your meds? I say yeah, four large cups of Cafe Bustello. JJasili, that Heath kit vttm is awsome, I am watching a turorial now on rebuilding one. I probably could put on my bench without the misses noticing
-
:angel
-
Have you ever used a different model Heathkit VTVM? or Brand? I looked at some of the other names you mentioned
-
No. But I have an Eico 221 that needs refurbishing internally. Externally it's a beauty. This Eico model is from the "Blue" period. Gorgeous with a "hammered" blue faceplate & gray wrinkle finish case. Meter is beautiful too with a real glass cover. The Eico is a tad larger than the Heathkit & doesn't fit on my shelf. Your wife will notice a blue Eico. She might even want one of her own! :l4:
Aside from cosmetics the brand doesn't matter as they all work off the same circuit. Heathkit has a clever probe with a SW-able 1M series resistor built in. This eliminates the need for for different probes using different input jacks.
Anyway I got a Heathkit IM-18 and liked it. So I got a total of 4. With 4 VTVM's I can simultaneously monitor the plate & screen voltages on 2 power tubes. It's easy at a glance to see if the needles are in the right place. For other other test points & floating readings I have 3 Fluke 8000A DMM's.
-
I tried explaining some stuff and after about five minutes she started laughing. She said its ok, I believe what you say but I might as well be speaking Klingon. This is sweet
-
> Have you ever used a different model .....
They are all 99% the same.
Once you use one a while, moving to another is mildly upsetting, like when the living room is rearranged. You get over it.
While there may be some differences in max and minumum ranges, at this late date, the important thing is that it works good. (Since all the sellers claim "no way to test", it's pot-luck.)
-
Im still rearranging my “bench” and shelves and in no rush. Ill only buy one that is either certified or garenteed. I have two sources I can look into
-
Chipping away at finishing up the meter. I took resistor measurements again without lifting them from the board. R24 is in series w r25 so that came out off. I used 3 9volt batteries for now to get me to 30volts. So far measurements are good but I want to send my fluke out for calibration and then compare.
-
always nice to see old meters come back for more! nice job