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Dirty-South Blues Harp forum: wail on! >
Lectrolab R500
Lectrolab R500
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HawkeyeKane
1098 posts
Aug 01, 2012
7:40 AM
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My bandleader just scored one of these old girls off of one of his usual attendees at his weekly open jam last night.
I've been reading up on the Lectrolab name lately. For you who aren't familiar with them, these were manufactured buy Valco's fellow Chicago instrument maker, Sound Projects Company of Cicero. All accounts say that SPC operated from the 1930's to the 1960's, but no exact years can be deifinitively established. Like Valco, SPC made guitars (HB electrics, lap steels, and triple neck steels in SPC's case), a variety of amp models, at least one reverb unit, and an early fuzz pedal that was based heavily on the Gibson Maestro. Also like Valco, SPC's Lectrolab brand was rebadged for other companies, namely Harmony.
Anyways, the one my bandleader bought...the R500.
2 12AY7 preamps, 1 5Y3GT rectifier, and 2 6V6 power tubes. A 12" Jensen Special Design. Two channels with individual volume controls, three inputs, and a tone knob. Pretty solid design.
I have yet to see or play it, but he did mention a few things to me over the phone. Said the amp takes a good two minutes or so for the amp to warm up. A little bit of a droning buzz in the speaker. I'm very anxious to try it, especially considering some of the reviews I've read on it compare it favorably to an original Fender Tweed Deluxe.
A few questions for you ampaholics though (Greg, 5F6H, Rick...)
First, could the lengthy warmup time be due to faulty preamp tubes? 12AY7's aren't the stiffest tubes out there and God knows what kind of condition the current ones are in. What about something with a bit more voltage gain? 12AT7's? 12AX7's would be awesome, but that's quite a jump from the gain of a 12AY7.
Second, the buzz I'm guessing is probably either a tube or a bad capacitor somewhere. (Hopefully not the multi-section filter..) Would anyone disagree?
Lastly, and Greg this is kinda directed at you, the power cord is expectedly two-prong. Anyone know where the best lug point on this thing for a three-prong ground line would be?
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Hawkeye Kane
Last Edited by on Aug 01, 2012 11:25 AM
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Greg Heumann
1728 posts
Aug 01, 2012
8:02 AM
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Looks like a cool amp. Slow warmup and buzz - if the power filter caps haven't been replaced that's the place to start. Old ones are almost always weak, and that can put a big load on the rectifier tube.
For a 3 wire power conversion, lose the cap C10 and use that ground lug.
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/Greg
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HawkeyeKane
1099 posts
Aug 01, 2012
8:31 AM
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Thanks Greg! What about a preamp tube swap though? And I need to correct myself...one of the 12AY7's served as a split preamp between the two channels. The other is a paraphase inverter to drive the output.
There were three variants of this amp. R500, R500B, and R500C. R500B used the same rectifier and power tubes, but AX7's instead of AY7's, and the paraphase inversion was replaced by a cathodyne.
So would something with stiffer voltage be recommended in either the preamp or the inverter?
SIDE NOTE: Harpsucker has several videos demonstrating different Lectrolab amps. Check them out!
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Hawkeye Kane
Last Edited by on Aug 01, 2012 8:37 AM
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5F6H
1302 posts
Aug 01, 2012
10:24 AM
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Apart from the tone pot after the PI, it's quite Masco-like (but that hardly makes it unique, fairly generic circuits).
12A#7 tubes warm up in the blink of an eye, I'm with Greg on the filter caps, but also check that the 5Y3 really is a NOS US 5Y3, if it's Russian, or been replaced with a 5V4 a slow warm up is to be expected BUT either of these will also boost the operating voltages over a NOS US 5Y3.
Later models probably used 12AX7 because they were cheaper! ;-) 12AX7s will bump up the gain, maybe not useful, but it won't do any harm to try.
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Last Edited by on Aug 01, 2012 11:21 AM
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HawkeyeKane
1102 posts
Aug 01, 2012
1:22 PM
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Just checked her out on my lunch. Didn't take anywhere near as long to warm up today. Caps have got some charge back in them it would seem. I blew through it, and it sounds really nice! A little on the tender side for gainy distortion though...so a test run with some AT7's or AX7's will probably be in order.
Tube complement: 1 Sylvania 5Y3, 1 GE 6V6, 1 JAN RCA 6V6, and 2 12AY7's that I can't make out a manufacturer stamp on, but I did manage to find an origin stamp on them. West Germany. Safe to say they're probably Telefunken?
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Hawkeye Kane
Last Edited by on Aug 02, 2012 8:58 AM
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HawkeyeKane
1104 posts
Aug 03, 2012
9:37 AM
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Gonna bump this cause I need a question answered.
I'm planning to use this amp tonight at a gig. If I swap the preamp tube for a 12AX7, do I need to swap the inverter tube for an AX7 as well, or will it be fine with the 12AY7?
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Hawkeye Kane
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5F6H
1305 posts
Aug 03, 2012
10:18 AM
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They are reasonably independent of each other (for a given AC voltage the PI doesn't know or care whether it's being fed by an AY turned up, or an AX turned down...it just deals with what it gets, however clean/distorted the sound may be - that's your call), obviously a bigger signal from an AX in V1 will distort V2 and the power tubes earlier, but as long as you have a 12A#7 (or 5751, even 12DW7) in each socket, whatever sounds & works best is "right".
Are you not getting enough gain at full volume before feedback with the AYs?
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HawkeyeKane
1105 posts
Aug 03, 2012
12:09 PM
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"Are you not getting enough gain at full volume before feedback with the AYs?"
For a 12-15W amp...not really, no. Tried it with both my Cherry Bomb and my Turner-Astatic. Neither one really had enough balls to it. Wish I'd given my DM13 a try, but it has no v/c and it was a virginal run so I stuck to the bullets.
I'm probably going to go ahead and plug a 12AX7 in tonight and run a seperate bullet into each channel. Cherry Bomb for fatter and distorted stuff, and JT30+2 for brighter tone.
Maybe I'll see about a 12AX7 in V1 and a 12AT7 in V2 if I can get my hands on an AT.
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Hawkeye Kane
Last Edited by on Aug 03, 2012 12:18 PM
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5F6H
1306 posts
Aug 03, 2012
12:58 PM
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Fair enough, it's a fairly low gain amp, no cathode bypass caps, so I wouldn't be shocked if it was a bit loose sounding...don't be afraid to try a 12AX/AT/5751 in the PI and an AY in the preamp either.
It undoubtedly runs more volts than the schem shows, but say it actually runs more like 70vdc on the 12AY...a 12AX might still only be nudging 100vdc in V1 (pure guesswork on my part) and may be rather stodgy, maybe prone to choking at those low voltages, with grid leak bias? Your ears will tell if I'm off base though...I'm just thinking out loud re. "possible" 12AX pitfalls..
Good luck.
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HawkeyeKane
1106 posts
Aug 03, 2012
2:06 PM
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Thanks for your advice Mark! Appreciate it!
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Hawkeye Kane
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