- R500: 2-12AY7; 2-6V6; 1-5Y3GT
- R500B: 2-12AX7; 2-6V6; 1-5Y3GT
- R500C: 2-12AX7; 2-6BQ5 (EL84); 1-6CA4 (EZ81)
- Speaker: 1-12″
The Lectrolab R200, R300 and R400 are all firmly ensconced in the “student” amplifier category. They were single-ended designs with one 6V6 output tube, or similar. They were similar to a Fender Champ in this regard.
Lectrolab upped the ante with the R500, which sports a 12″ speaker. Like the R400B it has individual first stage channels for instrument and mic. Each of these use half of a 12AY7, and have their own volume control. The signal from the first stages are mixed and then sent through a paraphase inverter (another 12AY7). The inverter output drives a push-pull pair of 6V6 output tubes, with a shared tone control along the way.
The Lectrolab R500B replaced the paraphase inverter with a concertina, or cathodyne inverter, perhaps in a quest for improved fidelity. It also added a fourth input, which did not provide any further functionality, it still had two individual channel first stages, one for inputs one and two, the other for inputs three and four. The control panel remained the same, two Volume and one Tone control. I do not have a clear schematic for this one.
The Harmony H305A is the same amp as the Lectrolab R500B. Sound Projects Company must have produced these for Harmony.
The Lectrolab R500C adds another Tone control, so there is one for each channel. I do not have a schematic for this. The tube compliment has changed. You can see in the pictures below that the Lectrolab 500C has 9-pin tubes throughout, which means the 5y3 rectifier has been replaced with a probable 6CA4/EZ81, and the 6V6 output tubes with 6BQ5, 7189, or EL84. In addition, the R500C is reputed to have fixed bias output tubes (see below). All this makes it a very different amp than the R500 and R500B, although there is little cosmetic change. It is very probable that the R500C is electrically identical to the S500. You can see a schematic for that here, and a parts list here.
If a tweed Fender Deluxe is your kind of thing, you are probably going to like the R500. Quite a step up from the R300 and R400.
We have no schematic for the R500C. Please let me know if you have one pasted inside your amp! However, it is very possible that, like other Lectrolab models, the RxxxC model is identical to the Sxxx model. Therefore, the R500C may have the same circuitry as the S500. See the S500 page for photos of the S500 schematic and parts list.
Click on pics to enlarge:
LECTROLAB HALL O’ FAME!
Ex. 10 in the gallery above had this info on the page where it was listed for sale:
“I purchased this amp from Robert A. Irvine he is a friend of mine and an inductee of the Rockabilly Hall Fame. He is still a great player and singer and a great person to be around. Any case he was cleaning out his basement and found this old amp he used to use for small gigs and and jammin with friends.”
Robert Irvine was inductee #342 in the Rockabilly Hall of Fame. He wrote and recorded ” Fastest Short in Town (Blue Fly) ” and “Lonely One ” for Chicago label Presto Records in 1964. Listen to this video – It could be a Lectrolab you’re hearing! The sonic signature is very much in the Lectrolab ballpark.
All those amps… But it’s the little brown Lectrolab making all that noise:
Q: Is it possible to get a Lectrolab R500C for free?
A: Yes, if you are lucky!
It’s a shame Lectrolabs don’t get the respect they so richly deserve, but it can be a blessing for the astute. See an interesting article from a lucky man here:
Lectrolab amp breaks all the rules(from Robbie and Laura Reynolds at http://music.mylounge.com/t205184-lectrolab-amp-breaks-all-the-rules. 08-18-2006)
I had the pleasure of looking inside a Lectrolab R500-C and drawing a schematic of it. If you’re not familiar with this amp, it is one of the greatest super-blues-tone amps you can ever get. It has the deepest, thickest sound of any amp I’ve ever heard. Not only that, but it is also fairly loud before feedback.
The strange thing about this amp is that it breaks several of the “rules” that you hear about good harp amps. The preamp consists of two 12AX7s. It sounds great this way, so there is no need to switch to lower gain tubes. Our buddy Gerald Weber states authoritatively that cathode biased power tubes are the way to go for a harp amp, but the Lectrolab uses a very strange -15 volt bias supply taken straight off of one of the high power leads at the rectifier.
Another thing is the coupling caps. Everybody seems to agree that .1 uF capacitors let more bass through, but the Lectrolab uses .01 uF. Regardless of what anybody says about .01 uF caps, this is a very deep-sounding amp. Another rule that it breaks is the one about ground loops caused by using the chassis as a ground path. Things are grounded willy-nilly all over the place, and the filament leads aren’t twisted together. This is supposed to cause a hum nightmare, but the amp is almost silent.
I have an amp of my own design of a similar power rating and
configuration. It’s a pretty decent amp, but not as good as the ones I’ve been building lately, so it’s probably destined to be cannibalized sooner or later anyway. I’ve been thinking that I ought to turn it into a Lectrolab clone just to see if I could recreate the amazing sound of the original.
A note about “rules” – There are none. Here’s a few facts:
- Both cathode-biased and fixed-biased amps can sound great, or terrible.
- Reducing the coupler cap values can make low notes sound better, more defined.
- It’s possible to have an acceptable signal-to-noise level with many different grounding schemes.