Saqqara
6 posts
Mar 31, 2012
1:56 PM
|
Getting ready to do the Jim Rossen mods to revoice a VHT Special 6 for harp. At least part of them, much as Kingsley did.
Ordering components is the hardest part of these projects.
I have in hand 1/2 watt 5% carbon film resistors in the specified values. They are light brown, shiny and smaller than a benedryl. The factory resistors in the amp are a good bit larger, like a tylenol.(I have a cold). They are grey, and have a dull finish.
Will the ones I bought do the job? I did some googling before the job and it seemed there was some controversy but in the end it didn't matter that much, particularly as I am not restoring a vintage amp.
Can anyone describe what the VHT stock resistors are? Metal oxide?
|
Kingley
1944 posts
Mar 31, 2012
2:07 PM
|
I think those were the same type of resistors I used. They seem to work fine. I think that the original resistors are maybe Mil spec. Maybe Mark Burness will see this thread and enlighten us.
|
Saqqara
7 posts
Mar 31, 2012
2:33 PM
|
What service... sorry I had your name wrong.
You still have the Jim Rossen values, 56k R9, 100k R10, 1.5k R12, 10k R15?
I'm going to do that, and the switch on the C11 cap that I believe you just removed.
Picked up a GE JAN 5751.
I find my playing sounds best with the leftmost switch in the downward position and the mic tightly cupped.
|
Kingley
1946 posts
Mar 31, 2012
2:56 PM
|
Yes, I'm still using those values. I use either a JT30 with a CM99A86 element or a Shure 545 with it. Sometimes I'll use a Belcat digital delay when the mood takes me. I always plug into the high input and have the amp on it's high power setting, without the boost switch turned on.
The GE Jan 5751 is a great tube.
|
ElkRiverHarmonicas
770 posts
Mar 31, 2012
4:10 PM
|
It is crazy how much smaller components have gotten. I don't know jack about amps, but I do work on radios and know a little about circuits. I took a capacitor out of a Heathkit HW 100 transceiver from 1960s, the modern one I replaced it with was maybe half its size. Same for resistors, old one look like whiskey barrels compared to today's. The original was a 1/2 watt too, right? As long as the wattage and ohm values are right, put it in, electricity don't care how big it is. I dunno when thus amp was made, but if it's been a while back, a modern resistor of the same value will probably be smaller.
The controversy in radios is that it doesn't look original inside, it's about circuit board cosmetics, I imagine it's the same argument for amps, right? There can't be a change in how the circuit operates if all values are the same...and a resistor can be out quite a bit before you notice anything on the circuit... (although on the Heathkit, one went out that goes to ground and the radio caught fire, it was 999,400 ohms out of value, lol).
BTW, my Heathkit resto project will be in the May issue of Monitoring Times magazine.
----------
David
Elk River Harmonicas
Elk River Harmonicas on Facebook
"It's difficult to think anything but pleasant thoughts while eating a homegrown tomato." - Lewis Grizzard
"Also, drinking homemade beer." - David Payne
Last Edited by on Mar 31, 2012 4:30 PM
|
tookatooka
2875 posts
Mar 31, 2012
4:27 PM
|
@ElkRiverHarmonicas. As an ex-electronics design engineer, 10 years ago I was designing telecom and communications equipment where passive components like capacitors and resistors were just a bit bigger than a grain of sand. No wires, just metal caps at either end for surface mount soldering. Many resistors were actually printed on the circuit board using resistive inks and the values trimmed with lasers. Some of the Integrated Circuit chips I was designing with had 10 million transistors etched into the silicon no bigger the the nail on your little finger. That was ten years ago, goodness knows what it's like today at the cutting edge of Electronics.
When I was a lad I made a one transistor radio which was really no more than a crystal set with a one transistor amplifier. It was about eight inches wide, six inches deep and two inches high. That was just the chassis. It needed an aerial wire about fifty feet long strung up in the garden. I just about got shortwave but couldn't seperate the stations very well.
----------
Last Edited by on Mar 31, 2012 4:55 PM
|
ElkRiverHarmonicas
771 posts
Mar 31, 2012
4:39 PM
|
That is insane Tooka!!!! I was at the museum of radio and technology today, doing an article for the June issue of MT. They had a pre-Titanic era (1908) condenser that was shaped like a bucket, way bigger than a 5 gallon bucket, maybe 10 gallons volume, does the same thing as a modern Varactor diode that's smaller than a pill. I read somewhere recently somebody had figure out how to store information with atoms!
----------
David
Elk River Harmonicas
Elk River Harmonicas on Facebook
"It's difficult to think anything but pleasant thoughts while eating a homegrown tomato." - Lewis Grizzard
"Also, drinking homemade beer." - David Payne
|
tookatooka
2877 posts
Mar 31, 2012
5:03 PM
|
@ElkRiverHarmonicas. Yes It's a fascinating thing to watch electronics evolve. You may find this interesting. It's a great site.
http://www.sciencedaily.com/news/matter_energy/electronics/
----------
|
Saqqara
8 posts
Mar 31, 2012
6:33 PM
|
Elk, this is a newly minted tube amp, hand wired in China, some folks seem excited about it on this forum. None of that surface mount stuff... not even an etched circuit board. Big components.
I modified a Danelectro Fab Echo pedal this morning as inspired by isaacullah. That was quite another matter. Thankfully that mostly involved scraping off resistors the size of grains of sand, and putting a small dot of solder in their place.
It is amazing how far we've come in such a short time. I used to make tech predictions and people would laugh at me, but I would laugh last. These days... I have no idea what's next.
The irony is, often the next big thing is quite retro. Like amps you can actually tinker with.
|
Greg Heumann
1552 posts
Apr 01, 2012
9:23 AM
|
My second job out of school was working for 3Com - at that time a young company of 65 people who had just introduced the first Ethernet interface for PC's. It was a full size board (about 4"x8") that fit the first IBM PC. Prior to that, Ethernet boards were for mini-computers - and separated the controller logic on one board (which was about 14"x14") and the "transceiver" in another box - that was the part that physically connected to the cable. This first combined Ethernet interface was densely populated with chips on both sides of the board, and sold for $999.
Now, an Ethernet interface is built into most computers and printers, takes 1 or two chips, and adds almost nothing to the cost.
By the way, it is ALWAYS OK to use resistors of the same value but higher wattage than the original, and capacitors of the same value but higher voltage. Neither of these affects the circuit negatively in any way.
----------
/Greg
Last Edited by on Apr 01, 2012 9:25 AM
|
