Crate V18: Mods and Conversions

[TomDanMac]

Originally Posted by scihibmxer@juno

So that must be the fixed bias tap for the 6L6 tubes. I had one (v50), but sent it back, it was an early version and anemic, I think they had screwed up the power supply and running it at ~300 volts on the power tubes. My wife's cousin picked up the later model and it sounded like a true 6L6 amp, and voltages at rail in the preamp were over 300 volts. But it also had a charred resistor in the power supply (R103?), he got rid of his also...

That part of the circuit looks strange to me right now, but I am sure there is a reason why it is that way...a watt and 22 ohms translates to over 200 mA, and half of that current through each of the two 33k resistors (it's a series circuit) would be over 350 watts...ah, yes, it's HF AC...if I calculated correctly, at about 965 Hz the parallel 33k resistors and the 10nF capacitor have the same impedance, anything above and the resistors get less and less, and that supply's frequency is likely in the tens of thousands of Hertz...there's both AC (pulsed/chopped DC) and DC there in that section...and my circuit analysis skills are terrible, except that I am smart enough to know that they are terrible...the 22R and the capacitor form the AC path, and almost all the DC voltage between the diode bridge DB101 and Q103 is across the two 33k resistors in parallel with the capacitor...the 22R and the 10nF have equal impedance at over 700 kHz; at a guess of a tenth of that frequency for the PS, the capacitor's equivalent AC resistance is about 220 ohms...the resistor is the coal mine canary, maybe, and if the supply goes into some sort of frequency runaway that resistor fries, opens, as it takes a greater amount of the pulsed voltage...it's the same as a fuse, and if you make the wattage higher on R103, it defeats the purpose, and you have a fire...mainly guessing here...I think it would take an investigation of the data sheet for U101 to find out how to figure out the circuit's frequency...or throw a scope probe on it while it is running...but I am thinking that maybe that resistor's charred appearance means it is doing its job...and maybe someone can read this and correct me if I am horribly wrong...

[sofasquare]

Has anybody tried the Bogner mod?

[scihibmxer@juno]

Originally Posted by sofasquare

Has anybody tried the Bogner mod?

Still looking for a volunteer... (hint!)

[Grey Ghost]

Hi Steve, just found out about your mods and the potential of v18. Very excited to get my hands on one. Not familiar with amp mods much, but will inform myself. A few questions. I heard your SLO and Liverpool clips and they both sound great, but as a blues fan, which of your mods would you recommend? To my ears, Liverpool mod seems to be more bluesy. My current amp is DRRI, which I probably will sell (just got offered cash plus a few pedals). I play in the style of Albert King (my favorite guitar player), Freddie King, Peter Green, Billy Gibbons, and Jimmy Page for blues rock. Thanks for your infos.

PS Just heard your Blues Diamond from Blue Guitar, dig the sound (heard a lot of Gibbon, Albert and Freddie King sounds). I am listing to your tracks as I write. The sound from your tracks is what I am looking for. What amp/mod was it?

[StevieG73]

That guy that was doing V18 mods on eBay is back:

http://cgi.ebay.com/Mods-Crate-V18-1...item45f36204f2

Just in case anybody wants to know.

[jimijam]

Originally Posted by StevieG73

That guy that was doing V18 mods on eBay is back:

http://cgi.ebay.com/Mods-Crate-V18-1...item45f36204f2

Just in case anybody wants to know.

I have a crate V18 amp and wish I was amp tech savvy...
I would mod it in a heartbeat... only thing I have done was replace the speaker.
Is this ebay mod any good?

[TomDanMac]

Originally Posted by jimijam

I have a crate V18 amp and wish I was amp tech savvy...
I would mod it in a heartbeat... only thing I have done was replace the speaker.
Is this ebay mod any good?

Hi...some conjecture based on the other items listed by the same person leads me to believe that this is possibly Nick from Rocketfire Electronics...if so, and I have no personal experience other than having read this thread many times, he posted several helpful and thoughtful (in my opinion) messages here awhile back, and he received a couple of positive reviews from others in messages here for his conversion on this chassis (if memory serves)...the description on this eBay page is similar to what was described here as having been performed by this guy...I'll leave it to you to take it from there, but it sounds legitimate to me, based only on that...

For some reason the term "two-headed fire-breathing monster" is in my mind right now...hmmm? I may have read that somewhere else, but I "think" that was how one person described the amp after its conversion...that can't be a bad thing...

[TomDanMac]

Originally Posted by scihibmxer@juno

So that must be the fixed bias tap for the 6L6 tubes. I had one (v50), but sent it back, it was an early version and anemic, I think they had screwed up the power supply and running it at ~300 volts on the power tubes. My wife's cousin picked up the later model and it sounded like a true 6L6 amp, and voltages at rail in the preamp were over 300 volts. But it also had a charred resistor in the power supply (R103?), he got rid of his also...

In my inexorable quest for "all the answers" (lol) I have been reading about the Carvin X30 studio, only 30 watts from two 6L6 power tubes due to reduced B+, and some people really liked that amp...this switching supply in the V18 is starting to look like a bit of a gem right now...somehow cobble together a dual 6L6 arrangement and have two B+ voltages switchable (not on the fly) and with the original EL84 arrangement available you have 3 amps in one...Franken-freakin-fun!!

[TomDanMac]

Originally Posted by scihibmxer@juno

OK, there are two different projects listed here, the one with the pot is the post OT line out. It also has large resistors that totally cut the speaker out of the circuit. The other altoids box, without the pot, is the biridged T attenuator. The bridge T is a fixed gain reduction. You can get all the parts for the bridged T at Rad Shck. You need to make one, then adjust the values some to get the volume you want.

So I used the Post OT line out to send signal to the PA, the pot is to adjust the level of signal that is sent to the PA (throught a passive DI box). The bridge T attenuation I put speaker wires and male - female jacks so you just insert it between the amp and the speaker. I showed it with 2 R2s and 2 R1s because Rad Shark didn't have 10 watt 5 ohm or 10 watt 16 ohm.

Years ago I paid about $85 for a pedal, a big yellow box with a heavy duty footswitch and I think a 20 ohm pot (HUGE!) of about 100 watt capacity to use with my 6G4 Fender...it was crude and didn't take care of Z-matching as well, but it worked...there must be some way that a smaller value pot could be thrown in here to tweak this design, perhaps? Not zero to full, but maybe from full to down 18 dB or something?

I have been reading about some of the technology from London Power (I have no affiliation with them, but this stuff looks very interesting)...

http://www.londonpower.com/catalog/index.php

and the gmX in particular intrigues me...from another thread it seems that you use a small resistor in the cathode of the power tubes to track every nuance of the power tubes' signal output and then using transparent SS power amplification and the amp's own output transformer and speaker (I think?) you faithfully reproduce your low-wattage amp's tone at a much higher volume...and I have to wonder...

How much better is that than simply using a divider/pot arrangement after the output transformer and another power amplifier (except that it is small and self-powered/self-contained, I guess...juice the PS to 420 VDC, and you have a 50 watt amp weighing 30 pounds, or make a separate supply for the gmX and use a neo speaker and at about 40 pounds have a 150 watt amp that can throw out 125 dB SPL of blues-rock niceness)?

It certainly would be nice to have line or instrument-level signals that are fully faithful to what the output tubes are producing...I think the Vox Valvetronix does something like that, maybe? I am just mulling over the best way to use this with my modeler in those situations where I want all the effects available...and I might just end up getting a pedal or two anyway, in the end, I guess...

Progression is regression, and vice versa...

[zombiwoof]

Originally Posted by TomDanMac

Years ago I paid about $85 for a pedal, a big yellow box with a heavy duty footswitch and I think a 20 ohm pot (HUGE!) of about 100 watt capacity to use with my 6G4 Fender...it was crude and didn't take care of Z-matching as well, but it worked...there must be some way that a smaller value pot could be thrown in here to tweak this design, perhaps? Not zero to full, but maybe from full to down 18 dB or something?

I have been reading about some of the technology from London Power (I have no affiliation with them, but this stuff looks very interesting)...

http://www.londonpower.com/catalog/index.php

and the gmX in particular intrigues me...from another thread it seems that you use a small resistor in the cathode of the power tubes to track every nuance of the power tubes' signal output and then using transparent SS power amplification and the amp's own output transformer and speaker (I think?) you faithfully reproduce your low-wattage amp's tone at a much higher volume...and I have to wonder...

How much better is that than simply using a divider/pot arrangement after the output transformer and another power amplifier (except that it is small and self-powered/self-contained, I guess...juice the PS to 420 VDC, and you have a 50 watt amp weighing 30 pounds, or make a separate supply for the gmX and use a neo speaker and at about 40 pounds have a 150 watt amp that can throw out 125 dB SPL of blues-rock niceness)?

It certainly would be nice to have line or instrument-level signals that are fully faithful to what the output tubes are producing...I think the Vox Valvetronix does something like that, maybe? I am just mulling over the best way to use this with my modeler in those situations where I want all the effects available...and I might just end up getting a pedal or two anyway, in the end, I guess...

Progression is regression, and vice versa...

That box you bought most likely just used a big rheostat as a cheap form of attenuator, that type has been commonly used with low wattage amps in the past, it's not ideal, but sometimes adequate if you don't use it on a higher-wattage amp. I made a homemade version years ago, but it ended up burning up after I used it for a short time, probably the rheostat I used was under-rated for what I was trying to do.

Al