R700

The Lectrolab R700C looks like a great amp.  Early to mid 1960’s.  It has:

  • A pair of 12AX7’s and a pair of EL84’s
  • 15″ speaker (usually a Jensen C15P).  Some have a 3″ “tweeter”, some shipped without it.  My R700C has the baffle cutout for the tweeter, but no screw holes for it.  They either ran out of tweeters or came to their senses.
  • One channel, two inputs
  • Volume, Treble, Bass controls
  • Three stages of amplification into a concertina splitter.
  • 7189 (like an EL84) push-pull output stage, probably about 15 watts.
  • Negative feedback around the power amp to the cathode of the last preamp stage (similar to a narrow panel tweed Fender Super Amp (FE4-A) and others).

I’ve not seen any other Lectrolab “700”s except the “C” version.  Cabinet reputed to be solid pine but is probably plywood.

The Custom Kraft Electra Bass Amp (Model 800) is identical to the Lectrolab R700C except for cosmetics.  Custom Kraft was an exclusive house-branded product for the St. Louis Music company (SLM), one of the largest musical instrument distributors in the USA.  They did not produce any of thier own amps, but apparently had Sound Projects build at least this one model for them.  SLM launched the Crate amp brand in the 1970′s, and bought Ampeg in the 1990′s.

Click on pictures to enlarge:

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This is a Custon Kraft Electra, the same amp as a Lectrolab R700C:

8/24/10 – This amp just sold on ebay for $360USD.  See photos from the auction in the gallery above.  It is the only tweed, or tan colored amp in the gallery.  I defy you to find a hand-wired 2-EL84 15 watt to 20 watt amp with a 15″ speaker for a better price, unless it’s another Lectrolab!

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This is the sellers video of Ex. 5 above, which I bought 9/23/10 on eBay for $255USD.  This amp has some issues.  I will refurbish it electronically in the next few weeks, and will post the results when through.

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Example 4 (above) was sold in June 2010 for $325.00 on eBay. Seller in Citrus Heights, California.  Seller’s description included:

  • chassis stamped “May, 16, 1967”
  • original 15” Jensen Special Design speaker
  • additional 3” speaker, which was standard for this model
  • original leather handle
  • 23” tall by 19 ½” wide
  • The amp powers right up and sounds fantastic, with the volume, bass and treble controls working as they should, and the amp getting pretty darn loud when running a guitar through her. She’ll work as a bass amp too, and she has a cool, 1960’s bass sound, but don’t expect thundering bass tones. The amp really shines with guitar, with beautiful highs and lows, and a nice, mild break up near the top of the volume control

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From  a thread on http://www.thegearpage.net/board/archive/index.php/t-604982.html:

  • http://www.vintaxe.com/index.php has an amp catalog section, buy It looks to be a pay to download. They do have a forum devoted to obscure brands like Custom Kraft: http://www.vintaxe.com/catalogs_american_customkraft_1966.htm
  • Works great. Some prior owner has or had the cap can replaced.
  • My issue is the volume is quite low for a 15ish watt amp.
  • The Jensen C15P is in between a ‘Q’ and ‘N’ meaning it is near the higher power handling C12N. It has a ribbed cone.
  • That’s definitely the same as my ol’ 60s Lectrolab 700c (cept mine hadn’t been painted black). I really liked the amp & the speaker. That said, I would nudge it up a bit w/ TS-9 just to kick up the vol. & the treble, w/o adding much drive & seemed to work fine at brightening it up a bit while pushing it, too. While I really liked it, I also had & still have two other old Lectrolabs. One is a 700c, also, but has 2 Jensen c12qs & a 3″ tweeter–that amp is oddly sorta bright (& apparently quite rare). The other is a 600c which definitely has a much dif. circuit but a sim. tube compliment, but has got a lot of gain. Cool amps. I’ve never been able to track down a schematic of either.
  • with the EL84s installed, I have taken some measurements
  • V1A: plate – pin1 – 44vdc
  • V1B: plate – pin6 – 121vdc
  • V2A: plate – pin1 – 235vdc
  • V2B: plate – pin6 – 224vdc
  • V3: plate – pin7 – 513vdc; grid 1 – pin 2 – (-14vdc); grid 2 – pin 9 – 388vdc
  • V4: plate – pin7 – 512vdc grid 1 – pin 2 – (-14vdc) grid 2 – pin 9 – 387vdc

9 Responses to R700

  1. Robert says:

    I have a 2×12″ Lectrolab R700C combo amp – is this just a rehouse, or were these a production amp?

    • Alan C. McKinney says:

      The Jensen C””P`s and P””P`s are,by design, very low efficiency..For example:where a Jensen Q series may have a rating of 97db a P series has an efficiency rating of 93db. To the human ear every 3 db added, translates into twice the volume. If you substitute a Chicago Jensen Model C15N VS the stock C15P your amp will sound much louder. Of course,you can use any brand of high efficiency speaker such as-Celestion Vintage 30 @ approx.104db or many of the newer Eminence Redcoat or Maverick series.Their efficiency ratings are posted on their website. All efficiency ratings in this posting are approximate as the source of this info is my memory. Please use the proverbial grain of salt………….thefishinmusician.

  2. LectroLabTech says:

    bump
    No more discussion on the amps? Does anyone know how the tweed covered Lectrolab models might differ from the rest with regards to internal components?

  3. MarkJ says:

    Thought I’d tell you about my “Weekend Score”. While wandering through a Lafayette, IN flea market yesterday, I came across a Lectrolab R700C at a booth specializing in old audio gear. I wasn’t immediately familiar at the time with this brand, but immediately realized the amp was of 50’s or 60’s vintage just from its appearance. Most of the covering (originally tweed) had been previously removed (with the exception of the back) and the front grille had a large hole in it. However, the amp was otherwise in working shape although it definitely needed some TLC. After haggling a bit with the vendor, I snagged the amp by trading him an old Bulova watch + $105 cash. Nice. Results of an initial checkout: the Jensen C15P sounds nice although, as mentioned, the amp doesn’t sound particularly loud for an 15-20 watter. Jensen date code is 220531 = circa July 1965 amp production date. Looks like this beauty will be soon heading to my amp repairman pal for a checkout on the caps and tubes and general servicing. One obvious question: should I attempt recovering the cabinet and, if so, is there a source for the original tweed or, at least, a reasonable fascimile?

  4. alexage1 says:

    Hi Mark – Catalogs (see the Branding and Advertising page on this blog) called the tweed covering “Irish Linen”, a type of fabric that was (is?) used for hard cover books among other things. I haven’t been able to find linen identical to the Lectrolab covering, but I haven’t invested a lot of time looking. Search Google Images for “Irish Linen” or “Airplane Linen”. You may find something suitable. If you do, and you recover your amp, be sure sure to let us know how it goes, and send pictures!

    Thanks,

    George

    • MarkJ says:

      Hi George,

      Thanks for the tips. I’ll keep checking to see if I can find an exact (or at least close) match to the original covering. I’ve already been in contact with my amp repair buddy (he does a lot of work on Valcos too) and will keep you posted on our restoration as it proceeds!

  5. Eric T. says:

    Wow, what a great site! I got my R700C on Christmas Eve 1973 and just celebrated my 40th anniversary as a bass player. My folks bought it for me from a garage sale on my block in Chicago along with a Kent bass. The Lectrolab was my amp for over a year until I got a used Ampeg B15N. Much later I replaced the Jensen with something a little beefier, changed it to front mounting, took out the amplifier and sealed up the back to use it as a practice cabinet. This past fall I did a big refurb, putting a pretty hefty MCM woofer in, a Speakon jack, corner protectors and finally tuning the port Helmoltz style. It sounds great thru the biamped Yamaha/Crown rack from my big rig as the lower cabinet in my practice setup. I kept the original amplifier and Jensen. I’ll send some pictures of the refurb if you’d like to post them. Thanks for this fantastic trip through memory lane!

  6. Andy Falstad says:

    I recently scored a custom kraft head only. 3 knobs, 3 inputs with the aqua diamond faceplate. No tremlo. Was that only 1966? What was the model # of the one I have. I believe it was a bass head. Got it for around $100.00 this seems quiet too for a 2 6l6 amp,, maybe I’ll try fresher n os
    tubes.

  7. N F Mjellem says:

    I have a 1967 Custom Kraft 800C Amplifier, it was called the “Quake Maker” , with a pair of 6L6’s and a 15 inch Jensen speaker and the “aqua diamond faceplate”
    A couple of years ago I took it into the Billy Zoom Custom Shop in Orange Calif for an overhaul.
    Its my favorite 6L6 Amp for Guitar. I’m pretty sure that the circuit is the same as the Supro Thunderbolt Bass Amp, except that the CK has a treble and bass adjustment, which the Thunderbolt does not.

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